git-update-dirs: usage(): Wrap two long lines

3fe00caa-00e8-11e4-b35a-c80aa9e67bbd
git-update-dirs: If the repo has modifications, disable ga sync

af171d0e-00eb-11e4-b453-c80aa9e67bbd
git-update-dirs: Add -G/--ga-dropget option

a2ec21da-00ed-11e4-aa91-c80aa9e67bbd