#472 Rollback changes

[John Morten Malerbakken]

From time to time I find that I have been too quick
when I have approved a change made by some users.

I suggest a feature which gives the administrator the
possibilty to reverse an approved change.

The change which is rolled back should go back to its
"pending chage" state so that it can be edited before
it is approved again or can be deleted from the list of
pending issues.

(Sure, I could spend more time and do a more thorough
job, but even then I will make mistakes from time to time)