Backported fix for #7445 ([7458]) from 0.11-stable.
0.11-stable: Added XHTML outout validation, closes #7445. Thanks Remy.
Drop support for Python 2.3.
Ignore .mo files.
0.11-stable: Added missing `_` import.
Merged [7453] from 0.11-stable.
0.11-stable: Slightly improved `trac-post-commit-hook` inline documentation.
0.11-stable: Bringing the branch back to stable state.
Tagging trac-0.11.1
Backported r7449 from 0.11-stable.