Ignore only source file changes for translations

Do not propose a new patch set, if only the source files (.pot) have
changed and no translated po file was changed.

This will reduce the number of patches. Example:
https://review.openstack.org/#/c/119537/1

Change-Id: I3f21dd0bc4ddb0ae9d8732590b1824f6171d2d7f
Merge "Ignore only source file changes for translations"