Removed use of the deprecated function 'notify'
Tidy up of lib.php
CONTRIB-4067 - Query user table for necessary fields only to avoid 'column ambiguously defined' error in Oracle
Bumped the version required as the last commit uses a function that was introduced in 2.6
CONTRIB-4960 - Ensure grade item exists to avoid 'Invalid argument supplied for foreach()' error

Thanks to David Balch for reporting this and providing a patch.
CONTRIB-4961 - Allow certificate types to specify if they want the grade to have a prefix or not

Thanks to David Balch for reporting this and providing a patch.
Increased version number
Merge remote-tracking branch 'upstream/master'