Enable custom __GIT_PROMPT_DIR as an env var

I'd like to directly point bash to where I checked out the source code.
With this change I can customize at least the base directory with an environment variable while the default value is still there.
When no upstream is configured, the script behaves as if push.default=current
Adding virtualenv with git prompt
Merge pull request #5 from mrahma01/master

Virtualenv with git prompt
Merge pull request #1 from skuro/patch-1

Enable custom __GIT_PROMPT_DIR as an env var
Merge pull request #2 from pkok/master

When no upstream is configured, the script behaves as if push.default=current
Fetch new remote revisions every other GIT_PROMPT_FETCH_TIMEOUT minutes
(5 is the default)
Configuration for fish shell
Fix, pwd outside git is not working yet :(
Fix for pwd
Remove extra configs, cleanup
Rename, more compatibility with original version
Cleanup log
Fixes
Last fix :)
Proper  support for external __GIT_PROMPT_DIR
Refactor
Example image from bash and fish shell with git prompt
Better image
Refix image