Make messages translatable and more sensible.
Summary:
These exception messages & comments didn't quite match reality.
Fixed and added pht() around a couple of them.
Test Plan: I didn't test this :P
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley, #blessed_reviewers
Subscribers: Korvin
Differential Revision: https://secure.phabricator.com/D17578