Patch Set 2:

Of course it would be great to implment submodule support. As far as I know, however, there is currently no activity in this area. I would suggest the following:
1. we promote bug 314853 to a feature request
2. we point the other bugs to that one as duplicate
3. we use the code changes proposed here to inform the end users about the missing feature so that they won't have to create new bugs