Explicitly setting python to the homebrew-installed version

If this is not set homebrew *seems* to use Apple's default library.

Before the change we have
```
$ otool -L /usr/local/Cellar/mod_wsgi/3.4/libexec/mod_wsgi.so
/usr/local/Cellar/mod_wsgi/3.4/libexec/mod_wsgi.so:
	/System/Library/Frameworks/Python.framework/Versions/2.7/Python
(compatibility version 2.7.0, current version 2.7.5)
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current
version 1197.1.1)

/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFound
ation (compatibility version 150.0.0, current version 855.11.0)
```

And after the change we have
```
$ otool -L /usr/local/Cellar/mod_wsgi/3.4/libexec/mod_wsgi.so
/usr/local/Cellar/mod_wsgi/3.4/libexec/mod_wsgi.so:
	/usr/local/Frameworks/Python.framework/Versions/2.7/Python
(compatibility version 2.7.0, current version 2.7.0)
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current
version 1197.1.1)

/System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFound
ation (compatibility version 150.0.0, current version 855.11.0)
```