Notification of string changes

Author: Tim Hunt
MDL-76298 drag-drop questions: validate the questions are complete
Previously, it was possible to create drag-drop markers and onto image
questions without any drag items or drop zones. This was non-sensical,
and broke statistics calculations.

So, missing validation added, and random guess score calculation made
robust.


http://git.moodle.org/gw?p=moodle.git;a=commit;h=7ab289879a353199f46e79ce0548a106d803ef45
http://github.com/moodle/moodle/commit/7ab289879a353199f46e79ce0548a106d803ef45

+ 4.0 en [formerror_dragrequired,qtype_ddimageortext]
+ 4.0 en [formerror_droprequired,qtype_ddimageortext]
+ 4.0 en [formerror_dragrequired,qtype_ddmarker]
+ 4.0 en [formerror_droprequired,qtype_ddmarker]