extensions: fix wrapcommand/function of class instance
5361771f9714 changed _updatewrapper() to copy the __name__ attribute, but
not all callable objects has __name__.
Spotted by loading mq with extdiff.
$ cat > abortcommit.py <<EOF
> from mercurial import error
> def hook(**args):
> raise error.Abort("no commits allowed")
> def reposetup(ui, repo):
> repo.ui.setconfig("hooks", "pretxncommit.nocommits", hook)
> EOF
$ abspath=`pwd`/abortcommit.py
$ cat <<EOF >> $HGRCPATH
> [extensions]
> mq =
> abortcommit = $abspath
> EOF
$ hg init foo
$ cd foo
$ echo foo > foo
$ hg add foo
mq may keep a reference to the repository so __del__ will not be
called and .hg/journal.dirstate will not be deleted:
$ hg ci -m foo
error: pretxncommit.nocommits hook failed: no commits allowed
transaction abort!
rollback completed
abort: no commits allowed
[255]
$ hg ci -m foo
error: pretxncommit.nocommits hook failed: no commits allowed
transaction abort!
rollback completed
abort: no commits allowed
[255]
$ cd ..