FIX: add support for rpath patching in OSX

The code adds rpaths to allow local relative libraries to get loaded at
link time, for linux only, using the patchelf binary.  This commit adds
some routines to do the equivalent thing in OSX, using the ``otool`` and
``install_name_tool`` binaries.
FIX: add some workarounds for OSX problems

Look for shared libraries ending in ``dylib``.

Add a header path to cmake for Qt framework.
Merge pull request #3 from matthew-brett/osx-fixes

Osx fixes