Check that all po/pot files are valid

Perform minimal checks on po and pot files so that no broken files can
get imported.

Change-Id: Ib438faddb362eb8e61eaa64a870160196f16c594
Related-Bug: #1299349
Co-Authored-By: Clark Boylan <clark.boylan@gmail.com>
Merge "Check that all po/pot files are valid"