leftover, the error handling of unlink() a couple of lines below used to carry a similar special-casing but was dropped; drop it here too.

This wraps the cleaning up of loose objects and redundant pack files under a new functions, making the _prepare() and _complete() functions unnecessary. It walks the reachable commits unconditionally since that information is always needed and adapt how we purge loose objects after this change. The progress function is changed too and we log `ncommits' first, followed by the number of loose objects, followed by the rest. Pack files are now considered redundant when all their objects are provided by a bigger pack or are unreachable. ok stsp

This provides better symmetry with 'gotadmin dump', and allows us to pass the list of references as command line arguments, replacing the -b option. The -l option now takes an argument which specifies the bundle file rather than requiring data to be fed on stdin with -l which feels awkward. ok op@

the newline is only needed after the progress output, which is not present in the 'listing refs' case.

it is intended to be the counterpart of `gotadmin dump' and, just like it, there's planned support for handling fast-import stream. At the moment it only deals with git bundles. ok stsp

set err and goto done instead of an early return that leaks various things. ok jrick

ok jrick