Fixes include path failure.

[turnage]

Attempting to use the library headers from their make install location results in <pokereval_export.h> being unfound. If make-installed, the location implied by the chevrons would be <poker-eval/pokereval_export.h>, though I think the standard method is just a relative path.

This is also a problem in the libpoker-eval-dev package, but I'm not sure if this is the same project.

Steps to reproduce:

1. Check out poker-eval.

2. Build and make install according to readme:

   autoreconf --install ./configure make ./configure make install

3. Create a compile-able c program and #include <poker-eval/poker_defs.h>

4. Attempt to compile.

Perhaps this is the wrong header to include? I am using it because I saw it in the examples.