Building help files use only master branch
When testing translations for help files, the new 'Build help' feature will use modules' master branch even when translation is taking place for a different branch.
Steps to reproduce:
- Upload a 100% translated help file of module's non-master branch to D-L
- Click "Build help" button to make the translated help available
- Access the help built and look for unexpected English strings
- Find the English strings in the module's master branch .po file in D-L