Instructions for creating an OS X native development environment

Probably not 100% complete yet, but covers enough to pass all specs.

NOTE: requires either libXML2 2.7.6 or the separately submitted fix to
pretty_text_spec.rb
The wrong version actually got moved to this branch when I tried to clean some things up. This version should be correct :-)
Merge pull request #642 from mshappe/mac-native-guide-fixed

Instructions for creating an OS X native development environment