Update CHANGELOG and configure.ac for the 0.68.1 release

Remove some code which was in a previous revision but isn't needed any more. It's unclear how this crept back in as there were no conflicts around this.

Update CHANGELOG and configure.ac for the -portable 0.68 release.

Remove direct included system headers which are included portably at ./configure time.

ok op@

Move pack progres object accounting to a single place. This makes it easier to account for the case were only loose objects are packed. A wrong amount of objects was reported before when packing loose ones.

This fixes a common issue when for e.g. generating patches with $ diff -u foo.orig foo where 'got patch' failed because 'foo.orig' has an 'unexpected status'. prodded by naddy, ok stsp

check_file_status used got_worktree_status to check if the file was in an allowed state, but it's wrong since the callback is not invoked on unchanged files. While here also fix a relate bug: unlink(newpath) is in the wrong spot and ends up removing files even when it shouldn't, so move it early in the got_worktree_schedule_* error handling. Finally, update the appropriate test case. It was passing before because got_worktree_schedule_add returned GOT_ERR_FILE_STATUS, not because check_file_status failed. ok stsp@

ok stsp