t/*: rearrange tests into numbered directories.

It was getting way too ad-hoc in there.  Let's reorganize the tests so that
there's a good, obvious, suggested sequence to run them in.

t/120-defaults-flat/default.b.do

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