MDL-29667 Plugins overview shows incorrect availability for auth & enrol plugins

We store the enabled plugins as array values but later look them up as array
keys. Just flip the array when we build it.
MDL-31527 XMLDB Editor - make sure default tables are created with correct plugin prefix
MDL-29402 QandA forum questions should be emailed
MDL-30709 mod_assignment: Renamed callback to mod_assignment_get_file_info
Automatically generated installer lang files
MDL-31495 Performance improvement in question engine upgrade SQL
[MDL-31386] Correctly order answers in a lesson backup
MDL-30388 Blocks: Search view for block instances fixed, with proper page url and pagination
MDL-30388 Blocks: navigation block is visible on block search page
Merge branch 'wip-mdl-30388-m21' of git://github.com/rajeshtaneja/moodle into MOODLE_21_STABLE
MDL-30888 course-search: Fixed typo
MDL-30495 HTML5 apps cannot call Webservices functions if a HTTP resource is retrieved from the Moodle installation
MDL-31556 Lesson Module: fixed missing 'lesson closes' event in calendar
Automatically generated installer lang files
Merge branch 'install_21_STABLE' of git://github.com/amosbot/moodle into MOODLE_21_STABLE
weekly release 2.1.4+
MDL-30830 dock: Added the title using accesshide for screen readers
SCORM MDL-31397 - add slashes to js string
MDL-31652 SCORM - hide updatefreq setting and remove it if not required.
MDL-31627: Arialist theme do not resize content when there are no blocks