Update gitfiletree for better cross-platform support, new issues(up to 102) and tests

This is a fairly large update, with:

* Small improvements to gitfiletree,
* Better portability,
* Scripts support (issue102),
* Activation of all new test cases (91, 92, 97, 102)

If this works, it should be a lot easier to try it on other platforms (Squeak:))