Fixed recursive import bug, git bug #49: https://github.com/leo-editor/leo-editor/issues/49

The problem was that g.os_path_join automatically called os.path.expanduser, which converts ~ to the users home directory.

The fix was to disable the call to os.pathexpanduser in g.os_path_join & g.os_path_finalize if the new expanduser keyword argument is False.

Leo build: 20140917180028