add password support for redis connects in cache and session

Thanks to Jetha Chan for providing the initial patch that this is
based on.

pgbouncer doesn't accept the PostgreSQL options command as it can't
process it.  If you are using pgBouncer you need to make sure your
database is configured to set client encoding and standard_conforming_strings
correctly on each connection.  pgBouncer can do this, as can ALTER
commands.

Also using sockets without a filename did not allow different ports to work.
This is because you either specify a filename which includes a port or
you just specify a port and libpq works out the correct socket location.

To support PHPUnit we need to support large profiles, these may
include backups and restores. To do that the following was required;
- gzcompress for database space saving.
- gzcompress for XML DomDocument field to say < 10Mb and allow imports.
- Save PHPUnit runs directly to a file so they can be imported to the normal database.
- Memory allowance on profiling view pages increases to support large profiles.

dirname() is a slow function compared with __DIR__ and using
'/../'.  Moodle has a large number of legacy files that are included
each time a page loads and is not able to use an autoloader as it is
functional code.  This allows those required includes to perform as
best as possible in this situation.

This reverts commit 15a813cd, reversing
changes made to 6870e1fa.

It is now possible to set up Redis as a session handler for Moodle.
Ensure that the phpredis extension is enabled and working on your sever.

Please place the following lines in config.php
$CFG->session_handler_class = '\core\session\redis';
$CFG->session_redis_save_path = 'tcp://127.0.0.1';

To determine if it has been set correctly, navigate to
$CFG->wwwroot/admin/phpinfo.php and find following the strings in the
session block,

session.save_handler = redis
session.save_path = tcp://127.0.0.1

Most importantly it retains formatting better, and supports different charsets far better than pandoc.

This lets us convert between common office formats. E.g. docx -> pdf
html -> pdf, html -> ods.

This commit also updates assignment editpdf plugin to use this converter
on all compatible submission files.

This config will be supported to avoid broken configuration
in future. As this is limited, we need will still use
->behat_config to set config values which can't be set by
behat_profiles

AMOS BEGIN
 MOV [clamfailureonupload,core],[clamfailureonupload,antivirus_clamav]
 MOV [configclamactlikevirus,core],[configclamactlikevirus,antivirus_clamav]
 MOV [configclamdonothing,core],[configclamdonothing,antivirus_clamav]
 MOV [configclamfailureonupload,core],[configclamfailureonupload,antivirus_clamav]
 MOV [configpathtoclam,core],[configpathtoclam,antivirus_clamav]
 MOV [configquarantinedir,core],[configquarantinedir,antivirus_clamav]
 MOV [configrunclamavonupload,core],[configrunclamavonupload,antivirus_clamav]
 MOV [pathtoclam,core],[pathtoclam,antivirus_clamav]
 MOV [quarantinedir,core],[quarantinedir,antivirus_clamav]
 MOV [runclamavonupload,core],[runclamavonupload,antivirus_clamav]
AMOS END

    This enables a plugin to implement rewriting rules enabling
    'clean' or 'semantic' urls such as /course/COMP100/ instead
    of /course/view.php?id=1234

Brendan Heywood authored Feb 02, 2016 and Dan Poltawski committed Feb 09, 2016

When $CFG->divertallemailsto is specified, this allows a list of email
or domain exceptions to be whitelisted enabling easier testing by groups
of testers who don't share a single email address.

The admin setting updateautodeploy no longer exists. The two existing
config.php flags $CFG->disableupdateautodeploy and
$CFG->disableonclickaddoninstall merged into a single one.

The upgrade key can be defined in the main config.php as
$CFG->upgradekey.  If it is defined there, then its value must be
provided every time the site is being upgraded, regardless the
administrator is logged in or not.

This adds functionality to create individual request directories which can
be only be used for the current request. They are removed by a shutdown
handler.

Mike Grant authored Mar 10, 2015 and Eloy Lafuente committed Mar 16, 2015

Both $CFG->logsql and $CFG->dblogerror had no use in moodle core
since ages ago (just the former had one use for nothing). Good time
to get rid of both as they are 100% misleading.

1. Create behat datadir within behat_dataroot not at same level
2. Define suffix for link and not use hard-coded values
3. Renamed ns_parallel to run.php
4. Rename variables to best understand them
5. Added support for each run to specify db, prefix, rerun and profile.
6. Showing number of steps in each line of parallel run.

Uses a new optional config variable to define custom MIME types
in JSON format. Includes new API for accessing and modifying
this data.

Functionality by default does not change with this patch.
However spaces are no longer stripped when cleaning usernames IF
$CFG->extendedusernamechars has been set.

Also included 2 trim statements where small issues were found with reading
external usernames in that  were not filtered for trailing whitespaces.

Several reports have been made about the unexpected purging of entire
memcached servers when MUC is configured to use Memcache and caches
get purged.
This is expected and occurs because the memcache extenions don't
provide isolated containers. Moodle data is stored along side any other
data in the cache and when caches get purged all data gets removed
whether it belongs to Moodle or not.

The docs cover this point and here I've added notes about this to both
config-dist.php and cache/README.md

AMOS BEGIN
 MOV ['gspath','assignfeedback_editpdf'],['pathtogs','admin']
 MOV ['gspath_help','assignfeedback_editpdf'],['pathtogs_help','admin']
AMOS END

Some hosting providers have a requirement to prevent users making
modifications to the configuration of scheduled tasks as doing so may have
a negative impact not only on their own site, but also on the performance
of other sites (depending on host configuration). For example, if the
statistics or automated backup tasks were run every minute, this could have
a negative impact for other users).

This commit adds a session handler which works using memcache (without
requiring the memcached extension), similar to the support for
memcache within MUC.

This may be less reliable than memcached but we have been using a
similar approach on our system without problems. In case, I added a
warning in config-dist.php.