allow debug logging with DEBUG=1
patch library load paths if they are incomplete

Only on OS X.

link-time and run-time library paths can differ,
causing `--zmq=/some/prefix` to successfully link,
but not produce an executable that can be
used without DYLD_LIBRARY_PATH,
depending on how the linked library is compiled.

This patches any library linked as simply 'libfoo.dylib',
and replaces the path with '/full/path/to/libfoo.dylib',
so that it will load correction using `install_name_tool -change`.
Python 3.2 unicode workaround
Merge pull request #587 from minrk/install_name_tool

patch library load paths if they are incomplete