Support for default.*.do rules.

I *think* this was the last missing part from djb's spec.  Certainly it's an
important one for any real project.

t/default.b.do

@@ -0,0 +1,10 @@
+if [ -e "$1$2.a" -o -e "default$2.a" ]; then
+	redo-ifchange "$1$2.a"
+	echo a-to-b
+	cat "$1$2.a"
+else
+	redo-ifchange "$1$2.b"
+	echo b-to-b
+	cat "$1$2.b"
+fi
+./sleep 1.1