Fix missing return values and some error tests for empty index files
Patches from Dave Jones and Ingo Molnar, but since I don't have any
infrastructure in place to use the old patch applicator scripts I
am trying to build up, I ended up fixing the thing by hand instead.
Credit where credit is due, though. Nice to see that people are
taking a look at the project even in this early stage.
I needed this to make a "sparse" archive conversion from my old
BitKeeper tree data. The scripts to do the conversion are just
incredibly ugly, but they seem to validate the notion that you
can actually use this silly 'git' thing to save your history in.
The tool interface sucks (especially "committing" information, which is just
me doing everything by hand from the command line), but I think this is in
theory actually a viable way of describing the world. So copyright it.