macports support

[podhmo]

Hi.

(upstream repository is maybe abadnoned, so sending PR to your repository)

I'm using Macports on MacOS, and Macports storing re2 library's position is unexpected directory.

$ port contents re2 | grep stringpiece
  /opt/local/include/re2/stringpiece.h

So, installing pyre2 via your repository is failed.

$ pip install "git+git://github.com/andreasvc/pyre2.git@master"
...
    src/re2.cpp:312:10: fatal error: 're2/stringpiece.h' file not found
    #include "re2/stringpiece.h"
             ^
    1 error generated.
    error: command '/usr/bin/clang' failed with exit status 1

So, Adding /opt/local path to _re2_prefixes.

[podhmo]

Oh, sorry, same pull request is created already.
axiak#16

[andreasvc]

Thx, merged

[podhmo]

thx