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/350-deps/test1.do

@@ -0,0 +1,15 @@
+# force-rebuild t1dep
+redo t1dep
+
+if [ -e t1a ]; then
+	BEFORE="$(cat t1a)"
+else
+	BEFORE=
+fi
+../flush-cache
+redo-ifchange t1a  # it definitely had to rebuild because t1dep changed
+AFTER="$(cat t1a)"
+if [ "$BEFORE" = "$AFTER" ]; then
+	echo "t1a was not rebuilt!" >&2
+	exit 43
+fi