Move some bits from the libexec helper to the main process so we know if the patch was generated by git or not and finally document the automatic stripping of a/ and b/ prefixes added by git-diff(1). ok stsp@

This brings the rest of the regression test scripts in line with patch.sh.

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@