Merge bonus credits along with user stats; log changes to staff notes on both users.

Source user staff note text:
2013-06-30 04:23:32 - Stats merged into user.php?id=2 (test1) by lazyblum - Removed 50.00 GB uploaded / 20.00 GB downloaded / 1000.00 credits

Destination user staff note text:
2013-06-30 04:23:32 - Stats merged from user.php?id=3 (test2) - Added 50.00 GB uploaded / 20.00 GB downloaded / 1000.00 credits by lazyblum

Can tweak the wording if needed.