Now there is error() for "library" errors and die() for fatal "application"
errors. usage() is now used strictly only for usage errors.
Signed-off-by: NPetr Baudis <pasky@ucw.cz>

properly clear the reference count at init time. It happened to work
for me by pure luck.

Until it broke, and my unreferenced commit suddenly looked referenced
again. Fixed.

Which made fsck very quiet about objects it hadn't found. So add
it. 

We'll need to make things like these optional, because it's
perfectly ok to have partial history if you don't want it,
and don't want to go backwards. But for development, it's best
to always complain about missing sha1 object files that are
referenced from somewhere else.

This shows that I've lost track of one commit already. Most likely
because I forgot to update the .dircache/HEAD file when doing a
commit, so that the next commit referenced not the top-of-tree, but
the one older commit.

Having dangling commits is fine (in fact, you should always have
at least _one_ dangling commit in the top-of-tree). But it's
good to know about them.

pathnames in them. We're migrating away from that.

This will cause tons of warnings for the current "sparse" archive,
but hell, better now than later.

This is totally untested, since we can't actually _write_ things that
way yet, but I'll get to that next, I hope. That should fix the
huge wasted space for kernel-sized tree objects.

Once I do the reference tracking, I'll also make it print out all the
HEAD commits it finds, which is even more interesting.

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.

internal format.

This doesn't yet check the reachability information, but we're getting
there.. Slowly.

It doesn't complain about mine. But it also doesn't yet check for
inter-object reachability etc.