windows: fix for normalize creating `C:.`, and thus `C:path` paths

This is the second of two fixes for gl-modules/shader-school#58. Specifically, `path.normalize`, when called on  `C:`, produces `C:.`, which in the case of `path.join("C:.", "foo")` produces `"C:foo"` instead of the desired `C:\foo`. This is probably a bug in the `path.normalize` implementation in node as well, so I've included an opt out behavior if `path.normalize('c:') !== 'c:.'`.

Sorry for the multiple changes: when I ran the tests on Windows (XP) the network tests were broken.