Make tap_ref match similar code in update
Use Formula tap methods
Check File.file? first to avoid second stat()
Let File.expand_path also do the join
Use Formula tap methods instead of matching the path
Drop pointless string split
Remove redundant "which git" guards

There is always a git executable on PATH due to the git wrapper in
Library/Contributions/cmd. The wrapper will notify the user if there is
not a real git installed.
Update s3cmd 1.5.0-rc1
Fix sha1

Seems like `openssl sha1 s3cmd.tar.gz` does not give the right sha1 value
s3cmd: update 1.0.1 bottle.