libstree 0.4.2 (new formula)

Adds [libstree](http://www.icir.org/christian//libstree/index.html), a generic suffix tree implementation written in C. 

This library provides a fast implementation for some interesting string operations, solving the [longest common substring](https://en.wikipedia.org/wiki/Longest_common_substring_problem) and [longest repeated substring](https://en.wikipedia.org/wiki/Longest_repeated_substring_problem) problems in linear time with the length of the string and is also used as an example in Aaron Patterson's [Writing Ruby C Extensions: Part 2](http://tenderlovemaking.com/2010/12/11/writing-ruby-c-extensions-part-2.html) and in lian's [ffi-stree gem](https://github.com/lian/ffi-stree).
I've heard back from the maintainer and happily they are willing to create a new release that won't require build patches. I'll be working with them to get the libstree source onto github and patched and will remove the patch from this formula once the new release has been cut.