3.7 (min PHP 7.1) requires 3.2 (first version supporting PHP 7.1)

This just deletes all the upgrade steps previous to 3.2.0. Some
small adjustments, like adding missing MOODLE_INTERNAL or tweaking
globals can also be applied when needed.

Also includes an upgrade step to prevent upgrading from any
version < 2016120500 (v3.2.0) as anti-cheating measure.

Next commit will get rid of/deprecate all the upgradelib functions
not used anymore in codebase. (note there isn't any this time).

As a result of fixing the auth plugins config storage in MDL-12689, many
settings would be falsely reported as new ones by
admin/upgradesettings.php. We do not want to confuse admins so we try to
reduce the bewilderment by pre-populating the config_plugins table with
default values. This should be done only for disabled auth methods. The
enabled methods have their settings already stored, so reporting actual
new settings for them is valid.

Some auth plugins used to have a mix of the legacy style of plugin names
in config_plugins table (such as 'auth/mnet') and the new correct
style (such as 'auth_mnet'). Attempting to rename the setting plugin via
low level SQL UPDATE could lead to duplicate key violation.

The patch introduces a new helper function to safely migrate the old
settings to the new ones, eventually informing the admin about the
values mismatch.

This just deletes all the upgrade steps previous to 2.7.0. Some
small adjustments, like adding missing MOODLE_INTERNAL or tweaking
globals can also be applied when needed.

Next commit will get rid of/deprecate all the upgradelib functions
not used anymore in codebase.

- Added configurable setting for path to mimetex binary
- Moved language strings from lang/en/admin.php to lang/en/filter_tex.php
- Config settings now stored in table config_plugins and retrieved
through get_config
- Added upgrade step to move TeX settings to the config_plugins table
and delete settings from the config table

AMOS BEGIN
  MOV [configconvertformat,core_admin],[configconvertformat,filter_tex]
  MOV [convertformat,core_admin],[convertformat,filter_tex]
  MOV [latexpreamble,core_admin],[latexpreamble,filter_tex]
  MOV [latexsettings,core_admin],[latexsettings,filter_tex]
  MOV [pathconvert,core_admin],[pathconvert,filter_tex]
  MOV [pathdvips,core_admin],[pathdvips,filter_tex]
  MOV [pathlatex,core_admin],[pathlatex,filter_tex]
AMOS END

Prevent moodle_url error, cleanup entity encoding and decoding, disable tex source view when TeX and Algebra plugins disabled, localise TeX source popup and prevent phishing attempts, fix executable permission of Algebra pearl script, prevent image error in tex debug when Tex/Ghostscript not configured properly, fix copyright blocks and phpdocs, improve coding style, fix wrong source display link in Algebra filter.

This patch fixes incorrect password creating, updating and resetting, updating of user fields, unsupported auth plugins are correctly identified, modification of mnethostid is prevented, fixed problem with email duplicates, new password is generated for users without email, etc. It also includes coding style improvements, more inline docs, future TODOs and license information.

MDL-23232 added support for enrol_plugin->all_enrol()  which indicates plugin allows users to add new enrolments manually

MDL-21782 reworked enrolment framework, the core infrastructure is in place, the basic plugins are all implemented; see the tracker issue for list of unfinished bits, expect more changes and improvements during the next week

AMOS START
    MOV [sendcoursewelcomemessage,core_admin],[sendcoursewelcomemessage,enrol_self]
    MOV [configsendcoursewelcomemessage,core_admin],[sendcoursewelcomemessage_desc,enrol_self]
    MOV [enrolstartdate,core],[enrolstartdate,enrol_self]
    MOV [enrolenddate,core],[enrolenddate,enrol_self]
    CPY [welcometocourse,core],[welcometocourse,enrol_self]
    CPY [welcometocoursetext,core],[welcometocoursetext,enrol_self]
    MOV [notenrollable,core],[notenrollable,core_enrol]
    MOV [enrolenddaterror,core],[enrolenddaterror,enrol_self]
    MOV [enrolmentkeyhint,core],[passwordinvalidhint,enrol_self]
    MOV [coursemanager,core_admin],[coursecontact,core_admin]
    MOV [configcoursemanager,core_admin],[coursecontact_desc,core_admin]
    MOV [enrolledincourserole,core],[enrolledincourserole,enrol_manual]
    MOV [enrolme,core],[enrolme,core_enrol]
    MOV [unenrol,core],[unenrol,core_enrol]
    MOV [unenrolme,core],[unenrolme,core_enrol]
    MOV [enrolmentnew,core],[enrolmentnew,core_enrol]
    MOV [enrolmentnewuser,core],[enrolmentnewuser,core_enrol]
    MOV [enrolments,core],[enrolments,core_enrol]
    MOV [enrolperiod,core],[enrolperiod,core_enrol]
    MOV [unenrolroleusers,core],[unenrolroleusers,core_enrol]
AMOS END

From now on, all English strings use the new syntax. They are not
eval()'ed any more and the only valid placeholders are {$a} and
{$a->foobar}. No extra quotes escaping, dollar sign escaping and putting
double percent signs.

The modified files were exported from AMOS database repository in the
new syntax and were re-ordered by stringid. Standard GNU/GPL and PHPdoc
blocks are added. Where there was no copyright note so far, I added the
default one with Martin Dougiamas as the copyright holder.

Live long and prosper.

MDL-21693 Dropping _utf8 suffix from language codes and folder names; enabling new string managers - please note the transition is not yet fully complete because we need to wait for git to recognize the renames in cvs