Minor changes to pay.pl and paycollect.tt to allow writing off a partial amount
of a fine.
0) Go to the Fines tab of a test patron's profile
1) Create a fine if there are none (under the Manual invoice tab)
2) Go to the "Pay fines" tab
3) Press the write off button on the corresponding account line
Without patch, you'll be asked to confirm, but will not be able to edit the
With patch, you'll be able to edit the amount.
Followed test plan, patch worked as described. Also ran QA test tool and
modified files passed