filter-branch: use printf instead of echo -e

In order to echo a tab character, it's better to use printf instead of
"echo -e", because it's more portable (for instance, "echo -e" doesn't work
as expected on a Mac).

This solves the "fatal: Not a valid object name" error in git-filter-branch
when using the --state-branch option.

Furthermore, let's switch from "/bin/echo" to just "echo", so that the
built-in echo command is used where available.

Signed-off-by: Michele Locati <michele@locati.it>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: mlocati

git-filter-branch.sh

@@ -627,12 +627,12 @@ then
 				print H "$_:$f\n" or die;
 			}
 			close(H) or die;' || die "Unable to save state")
-	state_tree=$(/bin/echo -e "100644 blob $state_blob\tfilter.map" | git mktree)
+	state_tree=$(printf '100644 blob %s\tfilter.map\n' "$state_blob" | git mktree)
 	if test -n "$state_commit"
 	then
-		state_commit=$(/bin/echo "Sync" | git commit-tree "$state_tree" -p "$state_commit")
+		state_commit=$(echo "Sync" | git commit-tree "$state_tree" -p "$state_commit")
 	else
-		state_commit=$(/bin/echo "Sync" | git commit-tree "$state_tree" )
+		state_commit=$(echo "Sync" | git commit-tree "$state_tree" )
 	fi
 	git update-ref "$state_branch" "$state_commit"
 fi