git-delrembr: Push only one branch at a time to the remotes

This is muuuch slower, but git doesn't delete remote refs if some of the
remote refs don't exist. Probably some security feature, and that's the
way it should be.

bbc2f660-ed35-11e2-adee-0800274013ad
6b45181a-ed37-11e2-9f58-0800274013ad
git-delrembr: Add -h/--help option

3b2a3882-ed36-11e2-b33c-0800274013ad
Create tests/git-delrembr.t, tests only the -h/--help option ATM

5bbc8e4c-ed36-11e2-a5eb-0800274013ad