GaudiProjectConfig: Fix generated __init__ files to handle symlinks.

The __init__.py files generated from GaudiProjectConfig.cmake has
code like:

```
__path__ = [d for d in [os.path.join(d, '${pypack}') for d in sys.path if d]
            if (d.startswith('${CMAKE_BINARY_DIR}') or
 ```

However, if the working path contains a symlink, then the element in
sys.path may have the symlink, but the value from ${CMAKE_BINARY_DIR}
to which we compare it will have the symlink expanded.  Change to expand
any symlinks (using os.path.realname) in the paths from sys.path
before comparing.