Merge branch 'MDL-36741_m23' of git://github.com/markn86/moodle into MOODLE_23_STABLE
MDL-37467 Do not provide blog posts via RSS when blogging is disabled
Merge branch 'MDL-37467-blogs_23' of git://github.com/mudrd8mz/moodle into MOODLE_23_STABLE
MDL-35780 Administration: email display on user profile view page will respect user capability
MDL-32341 calendar: get_file_by_hash() expects a hash
MDL-34050: Lesson module: fixed matching answer format to use text
MDL-34050 Lesson module: Fixed undefined variable for $qtype
MDL-34050 Lesson Module: improved matching question logic for checking user response.  This patch will also resolved MDL-36343.
MDL-35885 - Wiki - add a legend element to the search wikis form
MDL-36616 repository: Fix direct linking to images in Flickr Public.
MDL-37413 Use correct variable in chooserdialogue
MDL-37313 Moodle XML import format should use draft file areas, not arrays
MDL-37313 Sample files with images for XML import
MDL-37420 rework pg schema (partial backport of 92b00c3)
MDL-37420 rework pg schema (partial backport take2)
Merge branch 'install_23_STABLE' of git://git.moodle.cz/moodle-install into MOODLE_23_STABLE
MDL-27164 groups Do not show multiple instances of the same role as multiple
weekly release 2.3.3+
MDL-37397 Test for a valid select in formautosubmit

Ideally we shouldn't get into this situation, but in cases where the
generated select element is incorrectly configured, we should try and
handle it gracefully with a warning.
MDL-37374 questions: use property_exists rather than isset

$a->field = null; isset($a->field) returns false, which is typical PHP.
I also improve the error handling a bit.