Expand devel installation docs for Mac OS X.

This commit:

* Adds a small section to the "Development Version" > "Installing Dependencies" about PyGame on Mac OS X.
* Adds a "Troubleshooting on Mac OS X" page containing expanded information about troubleshooting PyGame installation problems.

I know that the install docs are a bit scattered (issue #1128, bullet 8), so if there is a better/different way to add this info or a subset of it to the docs, please advise me on what changes are needed :)