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/defaults-flat/default.b.do

@@ -1,10 +0,0 @@
-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