add an option that forces compilation as gnu89

see also:
http://blogs.perl.org/users/jason_a_crome/2012/04/compiling-mod-perl-2-on-os-x-lion.html
Merge branch 'master' of https://github.com/mkalkbrenner/homebrew-biologis
update download URL
Merge branch 'master' of https://github.com/mkalkbrenner/homebrew-biologis