Fixes #6 - build now completes on OS X 10.8

Pulled in the changes from the homebrew [issue](https://github.com/mxcl/homebrew/issues/12567#issuecomment-6434000) with compiling libvpx.

Tested on OS X 10.8

```bash
sudo ln -s /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer /Developer
export XUGGLE_HOME=/usr/local/xuggler
export PATH=$XUGGLE_HOME/bin:$PATH
export DYLD_LIBRARY_PATH=$XUGGLE_HOME/lib:$DYLD_LIBRARY_PATH
ant run-tests
```