MDL-17458 upgrade logging implemented + a lot more refactoring + exceptions implemented in install/upgrade code + lang pack cleanup + some more improvements

MDL-17458 refactored guest and admin user creation + refactored roles install + added protection for installation hijacking + added reliable session test right before editting of admin account

MDL-17267 simplified create_role - not adding assign and override perm to admin accounts, they have it now always

accesslib: Nice debug developer warning if you call get_users_with_capability without including u.id in the list of fields.

MDL-17849 sql queries not printed by default during upgrade anymore, there is a new config.php only setting $CFG->upgradeshowsql instead

MDL-17776 added new define CLI_SCRIPT that identifies all CLI scripts + cron (cli scripts do not have session and do not like HTML in output and are executed from command line, cron is an exception)

MDL-17693: get_role_users - add lastaccess & mnethostid to the list of default fields to return. These are used by messaging/emailing. (Merged from MOODLE_19_STABLE)

MDL-17692: count_role_users now accepts an int or an array of ints for roleid - this is now consistent with get_role_users. (Merged from MOODLE_19_STABLE)

MDL-17647 was referring to moodle/site:candoanything insstead of moodle/site:doanything

MDL-17648 Let get_users_by_capability take an array of capabilities, like has_any_capability

MDL-17649 get_users_by_capability must have unit tests (HEAD only).

The unit tests were briefly working (apart from the system context, which I had to set up by hand in the test contexts table). Then I made the mistake of trying to upgrade the test tables, and it all went horribly wrong (MDL-17644).

MDL-17502 accesslib: added warning if incorrect parameters supplied to has_all_capabilities() and fixed parameters in course lib code

course categories: MDL-17502 when deleting a category and its contents, check moodle/course:delete capability.

* Note: this would never lead to problems with default role definions.
* Also ended up mostly rewriting delete_category_form to simplify the messages that are displayed.
* New helper function require_all_capabilities, a bit like require_any_capability.

Bugs: MDL-17479, MDL-16426, MDL-16063, MDL-16013, MDL-15658, MDL-15556, MDL-15161, MDL-14925, MDL-13742, MDL-11557.

* Simplify category editing permissions to just moodle/category:manage and moodle/category:seehiddencategories.
* Enforce those correctly. (Note MDL 17502 is still outstanding.)
* Don't screw up category sort order when you just edit name or description.
* Niceties like where redirects go when you cancel or submit forms.
* Make sure a global course creator can see the site admin block.
* Don't allow a category to be made the child of one of its children!
* General code cleanup to bring key files more in line with best pracitice.

Apologies for the fact it is one big patch, rather than a series of smaller patches. However, categoryedit.php, category.php and index.php where in pretty bad shape and needed significant cleaning up. categoryedit.php, in particular, was almost completely rewritten.

Merged from MOODLE_19_STABLE.

MDL-17372 admin reports: Added full plugin support for admin reports; added specail capability for unittest execution, minor refactoring

MDL-17372 admin reports: Added full plugin support for admin reports; added specail capability for unittest execution, minor refactoring

role assign: MDL-17323 Show users with the role in a parent context as disabled opitons in the existing users box

* Move the show/hide advanced button a bit down the page.
* Improve save button caption when creating a role.
* Don't show defaults on the basic define roles screen.
* Explain the background shading on the advanced roels screen.
* Fix the problem with the risks link to Moodle docs.
* Help icon by the permissions column heading.
* Tables with rotated <th>s, make them vertical-align: bottom.
* Rename explain.php and explainhascapability.php to check.php and explain.php
* Tool tips on the number headers in the explain table.
* Explain table - role names were missing.
* Allow link_to_popup_window to work with full URLs.

MDL-17267 roles, install: fixed allow role assign table duplicates problem during install - see tracker for more details

* New basic define roles mode, with just an Allow checkbox for each capability.
* Button to toggle this form to/from advanced mode.
* Also, a separate mode for viewing a role definition, rather than just showing disabled checkboxes.
* Now duplicating a role just takes to you a pre-populated add role form, so you can double-check things before saving the new role.
* Deleting a role is now logged.
* Role reordering code cleaned up.
* You can now no longer delete the last role that has admin permissions.
* This includes a general refactor of manage.php, which eliminates manage.html, and splits of define.php.

I have collected code that used to be in lib/adminlib.php, lib/accesslib.php and user/selector/lib.php into a new admin/roles/lib.php file.

And I added standard GPL and Moodle comments to all the files in admin/roles.