modify for cygwin
Make `gitbranch` aware of external .git-dirs

.git directories may reside outside of working-copy dir. In that case, the
git-dir path will be read from the '.git' file and canonlicazed with readlink.

Known bug: will not if cd'ing into subdir of working copy (because of .git
location).
Add cia, cob, rb, and rbm git aliases.

Add aliases for:

* `git commit -a`
* `git checkout -b`
* `git rebase`
* `git rebase master`

to both gitconfig and .alises for less typing during source control.
Test
Merge branch 'cygwin' of github.com:datamadsen/dotfiles into cygwin