Notification of string changes

Author: Tim Hunt
MDL-81612 assign: show current value when editing a student's extension
Also, if there is not currently an extension set, the set extension form
will default to whatever is the latest out of the due date, the cut-off date
and midnight tonight (in the server time-zone).


http://git.moodle.org/gw?p=moodle.git;a=commit;h=d5fe176df1073457a9c9b9b184209182e475ac3b
http://github.com/moodle/moodle/commit/d5fe176df1073457a9c9b9b184209182e475ac3b

+ 4.5 en [extensionduedaterange,mod_assign]
+ 4.5 en [extensionduedatewithout,mod_assign]