[CppAD] Homebrew formula for CppAD on OSX

[Dominique Orban]

I wrote a formula that lets users install and test CppAD easily on OSX using the Homebrew [1] package manager. I submitted it for inclusion in the Homebrew/Science tap [2]. I would greatly appreciate any feedback from OSX users.

The formula may currently be installed with the command

	brew install \
	https://raw.github.com/dpo/homebrew-science/b62327a038795f03c2541180a572b1cfc88b252c/cppad.rb \
	--use-gcc

Once accepted into Homebrew, it will just be a matter of `brew install cppad --use-gcc`.

The `--use-gcc` option forces compilation with gcc instead of clang (the default C/C++ compiler on OSX). Unfortunately, clang does not support OpenMP, which makes CppAD excruciatingly slow.

Please post any comments or feedback on the formula on its pull request page [3].

Thank you in advance and enjoy!

Dominique

[1] http://brew.sh
[2] https://github.com/Homebrew/homebrew-science
[3] https://github.com/Homebrew/homebrew-science/pull/440