Fix PEP-257 issues in the reviewboard/attachments module.

Review Request #7202 — Created April 14, 2015 and submitted — Latest diff uploaded

Information

Review Board
release-2.5.x
27486cc...

Reviewers

This change fixes existing docstrings and adds new ones for the attachments
module.

Ran pep257 --ignore=D100,D203 and saw only a few expected errors from our
special testcase docstrings.