.join() and .path.normalize() incorrectly interpret base paths ending /. or /..

When joining URLs, furl correctly treats a path `/a/b/c/d/../` as equivalent to `/a/b/c/`, but it incorrectly treats `/a/b/c/d/..` as equivalent to `/a/b/c` rather than `/a/b/c/` (with a trailing slash). This causes further path components to be joined at the wrong level.

```pycon
>>> furl("http://host/a/b/c/d/../").join("D") # correct
furl('http://host/a/b/c/D')
>>> furl("http://host/a/b/c/d/..").join("D") # expected furl('http://host/a/b/c/D')
furl('http://host/a/b/c/d/D')
```

A similar problem can be observed with `.path.normalize()`. This one also affects paths ending in `/.`:

```pycon
>>> furl("http://host/a/b/c/d/./").path.normalize() # correct
Path('/a/b/c/d/')
>>> furl("http://host/a/b/c/d/../").path.normalize() # correct
Path('/a/b/c/')
>>> furl("http://host/a/b/c/d/.").path.normalize() # expected Path('/a/b/c/d/')
Path('/a/b/c/d')
>>> furl("http://host/a/b/c/d/..").path.normalize() # expected Path('/a/b/c/')
Path('/a/b/c')
```