MDL-34182: Add functions to warn of output in AJAX scripts

We need to be able to capture output when including contributed code as it
may add additional content which makes makes the json we output invalid.

We only warn of these errors if the site is in debugdeveloper, otherwise
we silently drop them.
MDL-34182 Repositories: Check for and warn on invalid output in the file picker
MDL-35032 mod_book: 1.9 backup restore convertis files to book area
MDL-43250 Assign: separate groups mode fix

When in separate groups mode, only get graders in a group that is in the course module grouping.
MDL-30195 portfolio_googledocs: Allow export of rich HTML
MDL-43438 mod_assignment: Prevent double inclusion of plugin files
MDL-41246 cache: Fix PHP notice of non well formed numeric values for the memcache store
MDL-41788 theme_bootstrapbase: Custom menus - sub-menus breaking.
MDL-43318 Assign: Fix bug when editing previous attempt feedback

Conflicts:

	mod/assign/renderable.php
MDL-43367 stop returning of bogus context children when path unknown

This also prevents deletion of system context.
Merge branch 'MDL-34182-25' of git://github.com/andrewnicols/moodle into MOODLE_25_STABLE
Merge branch 'MDL-43318-25' of git://github.com/damyon/moodle into MOODLE_25_STABLE
Merge branch 'w52_MDL-43367_m25_contextpath' of https://github.com/skodak/moodle into MOODLE_25_STABLE
Merge branch 'MDL-30195-25' of git://github.com/FMCorz/moodle into MOODLE_25_STABLE
Merge branch 'MDL-35032-25' of git://github.com/FMCorz/moodle into MOODLE_25_STABLE
Automatically generated installer lang files
Automatically generated installer lang files
Merge branch 'MDL-43250-25' of git://github.com/damyon/moodle into MOODLE_25_STABLE
Merge branch 'MDL-43438-25' of git://github.com/FMCorz/moodle into MOODLE_25_STABLE
Merge branch 'MDL-41246-moodle25' of git://github.com/StudiUM/moodle into MOODLE_25_STABLE