Paths with spaces not handled for Python paths

Even when the environment variables `LIBDIR`, `GOPY_LIBDIR`, `LIBRARY` and `GOPY_PYLIB` are properly set and surrounded with quotes (even tried double quoting with the inner pair escaped) spaces in the path are not properly handled. I had to move my python installation from `C:\Program Files\Python3` up to `C:\Python3` to get a package to build.