Split cmd now processes commits in topo order.

Added the "--topo-order" option to git rev-list.  Without this, it seems that
the revision list is coming back in reverse order but it is sorted
chronologically.  This does not gurantee that parent commits are handled
before child commits.

git-subtree.sh

@@ -547,7 +547,7 @@ cmd_split()
 	# We can't restrict rev-list to only $dir here, because some of our
 	# parents have the $dir contents the root, and those won't match.
 	# (and rev-list --follow doesn't seem to solve this)
-	grl='git rev-list --reverse --parents $revs $unrevs'
+	grl='git rev-list --topo-order --reverse --parents $revs $unrevs'
 	revmax=$(eval "$grl" | wc -l)
 	revcount=0
 	createcount=0