We've had code in the tree for a long while to stamp Perforce changes

with a review request URL, but it had a flaw. It left out a newline,

causing the first line to read:

Description:   Here is the first line.
        And here is the second line.


This was due to a missing newline after adding the "Description:" field.
This change fixes this up, reworks the logic and comments to be a bit

more clear about the states being kept and the newlines added, and adds

unit tests.
It also fixes up the amending portion, which didn't include a changenum

in the p4 change command (which meant it couldn't amend anything but

default).
A timeout is now set for the p4 change command, in case anything fails

during a hook script. Errors are outputted if anything goes wrong.

Unit tests passed.
Tested manually with updates to the trigger script.