I had to do some hackery to get this building on 10.6 with Homebrew. I
mostly hacked together a fake nspr.pc and dropped it in [1] so that
the pkgconfig stuff in setup.py would work. There's a copy of this
file in the "extra" directory in this repo. I also added a patch
for the va_copy like MacPorts does.

If anyone would like to tear out the embedded copy of Spidermonkey
that this package ships with and update the build system to use
either what Homebrew installs or is found in the xulrunner package
on Ubuntu, that would be awesome.

[1] /usr/local/lib/pkgconfig/nspr.c