Historically it was possible, through a series of question restores,
moves and edits, to end up with multiple questions in the same
category with the same stamp, but differences in other question
or answer fields. This, combined with changes in versions, led
to errors when restoring or duplicating quizzes using these questions.
While recent changes have made it impossible to create this situation
in current Moodle versions, as any edits will create a new question
version with a new stamp, this situation may exist on long-standing
Moodle sites which have been upgraded since pre-4.0.
This change performs a much wider-ranging comparison of restored
existing questions, generating a hash of all the data for a question in
a backup file, and a corresponding hash for each question in the target
category, to decide if a restored question matches a question already in
the database.
Mark Johnson
c6f329808c