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/atime2.do

@@ -1,6 +0,0 @@
-# make sure redo doesn't think merely *reading* the old file counts as
-# modifying it in-place.
-cat $1 >/dev/null 2>/dev/null || true
-./tick
-cat $1 >/dev/null 2>/dev/null || true
-echo hello