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/101-atime/tick

@@ -0,0 +1,6 @@
+#!/usr/bin/env python
+import time
+
+t1 = int(time.time())
+while int(time.time()) == t1:
+    pass