The homebrew instructions were outdated - berkeley-db4 hasn't worked for months, based on the questions I'm seeing on Google/SO. So I added a section explaining how to install berkeley-db4 using homebrew and move on with your life. Thanks for the rest of the documentation!
* reformatted the entire document to look pretty in both standard text and
Markdown
* incorporated [my OS X 10.8 build instructions with Homebrew as the package
manager](http://bitcoin.stackexchange.com/questions/3672/trouble-compiling-bitcoind-on-osx-with-homebrew/5253#5253)
* incorporated @gavinandresen's MacPorts and release build instructions based on
an earlier revision of this commit
* added makefile patch necessary for Homebrew compilation to `contrib`
Rose Toomey