Update saltstack formula to work with a recent version of homebrew

- Bump saltstack to 0.10.3
- Add folders that could host virtualenv to path
- Add build dependency on swig - required by M2Crypto python module
Updated salt to 0.10.5
Updated README
Use homebrew python
Patch salt to put configs, logs, etc under Homebrew
Remove virtualenv dependency

Require Python modules using the depends_on => :python interface
Merge pull request #1 from singingwolfboy/master

Updated formula
Add arguments to installation formula so all files end up in Cellar

https://github.com/mxcl/homebrew/wiki/Homebrew-and-Python
Automatically install dependencies if --with-deps option is passed
Embed patch into the formula and use HOMEBREW_PREFIX instead of hardcoded /usr/local