Used @property decorator when possible

I didn't touch property() that were applied on method without the "_" prefix, since I suppose there are part of the public API and should remain accessible as methods.

So really, I just modified 3 properties, it's not much but hey, incremental improvement ^^

By the way, I ran the unit test with python 2.5, 6 and 7 fine, but running it with 3.2 gives me the following error:

``` 
python3 test_path.py 
  File "test_path.py", line 97
    self.assert_(x == u'xyzzy')
                             ^
SyntaxError: invalid syntax
```