Building on OSX with Homebrew and a virtualenv - WIP

[SkyLeach]

I've managed to get this mostly working, however there is still some work that needs to be done.

I'm starting this issue to link and track my fork until the PR is ready and to discuss issues related to it.

[SkyLeach]

I had everything working until I updated panda3d.

| => python
Python 3.6.4 (default, Jan  6 2018, 11:51:15)
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.39.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import panda3d.core
>>> import panda3d.lui
Invalid TypeHandle index 222!  Is memory corrupt?
Assertion failed: (pnode != (TypeRegistryNode *)NULL), function record_derivation, file dtool/src/dtoolbase/typeRegistry.cxx, line 160.
Abort trap: 6

I think this is related to the newest panda code or some of the thirdparty libs. I will play with it a bit more to try to find out.