Update to make all git fetching consistent.

This commit should resolve #1 (closed). The behaviour of aaoBuildFetch is changed such that it will always try to fetch from origin, even updating the origin URL itself. (Updates to the origin URL might happen in practice if the .cfg file changes). But it also ensures that origin/HEAD always works (even on repositories without an origin). We resolve this to be that subsystems and the system itself will always be kept up-to-date except for one reason: If the system doesn't have an origin in it's git repo, and a URL isn't given on the command-line. ff-only pull stuff is completley removed as it's not nessecary, because I made the URL optional to fetchFromGit function. subsystems should now use origin/ or or origin/HEAD for the subsys.Checkout line