mxcl/homebrew — pull request #11883 by 2bits (2012-04-25 22:34:40+00:00)
Title: Imagemagick: add libxml2 for Mt. Lion

Imagemagick-6.7.5-7 uses libmxl2, but Apple changed the file
`xml2-config` starting in Mt. Lion, removing the `--prefix` flag.
That breaks imagemagick, which uses it to find the library.
Both Homebrew and Mt. Lion use libxml2-2.7.8.
Add a dep on libxml2 if Mt. Lion. This fix needs confirmation
that it works as intended, as Mt. Lion is not available to the
author.

Should fix #11789