MDL-31000 Respect sortorder of repositories when displaying the filepicker
MDL-31160 block_navigation: Fixed incorrect thrid arg to substr.
MDL-31197 navigation: Fixed issue withing require_login for courses that are hidden or unavailable
MDL-26260 quiz 'secure' window: close loophole in some themes.

Some themes put padding on body, which meant there were a few pixels
where you could get at the context menu. Oh noes!
MDL-31319 quiz attempts: include currentpage in backup
MDL-31267 update mymobile login page
MDL-31392 qeupgradehelper partial upgrade support broken since 2.2
MDL-31360 Don't use get_in_or_equal if array is empty, tidy up structure of $extracaps array
SCORM AICC MDL-31039 update external AICC url correctly - thanks to Albert Rhemrev for report/fix
MDL-31317 original_site_identifier_hash falls back to null during the backup conversion

Even if the site identifier is not defined in the source 1.9 backup then the
converted 2.0 version should still contain the element to prevent PHP
notices on direct assignment.
MDL-31311 Enhance unhelpful iframe title attributes
MDL-31015 File/URL resource 'Open' and 'Force download' options should work consistently
MDL-31314 gradebook restore: fix category.depth on restore.

Without this, restoring backups made with the OU's custom 'restore from
1.9' feature, and possibly other people's custom converstion code, does
not work properly.

Also, fix poor recordset code.
MDL-30854 quiz/question editing: fix create calc question & add on page.

This was one of those innocent seeming issues where, once you start
digging, you find a mess. In this case, the code that is now in
question_wizard_form::add_hidden_fields used to exist in four different
places, in four inconsistent versions. This is now all nicely
re-factored, and that solves the problem.

Along the way, I found and fixed some wrong string references in
qtype_random, and stripped out some unnecessary &s in function
declarations.
MDL-30484 question engine: don't lose response files when regrading.

The problem was mostly that, in the past, we did not worry if
question_attempt_step.id changed during regrade (because we deleted the
old step row and inserted a new one). However, now that steps can have
associated files, we can't be that slack, becuase the step id is used as
the file itemid.

So, now, we have to update the existing rows during a regrade. We do
this by having the question engine tell the question_engine_unit_of_work
that the step has first been deleted, and then added back. Then we make
the unit-of-work spot that delete + add = update.

This also means that during regrading, we have to pass around some extra
ids so that new steps know the id of the step they are replacing.

Naturally, this requires some quite trickly logic, so I finally got
around to writing unit tests for question_engine_unit_of_work, which is
a good thing.

Along the way I also got around to renaming
question_attempt->set_number_in_usage, which got missed out when
everthing else was renamed to slot ages ago.

Finally, while working on this code, I noticed and fixed some PHPdoc
comments.
MDL-31426 forum: don't show/allow any subscription to not enrolled users
MDL-31428 forum: prevent some warnings with debug enabled
MDL-29097 course: refactored to avoid having two seperate calls to events_trigger()
MDL-29615 message: added the ability for admins to restrict users ability to set where their email message notifications go
MDL-30828 mod_feedback: fixed sorting when viewing responses