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/deps/gentest.do

@@ -1,21 +0,0 @@
-rm -f genfile2 genfile2.do genfile.log
-
-echo echo hello >genfile2.do
-../flush-cache
-redo genfile1
-
-# this will cause a rebuild:
-#      genfile1 depends on genfile2 depends on genfile2.do
-rm -f genfile2.do
-../flush-cache
-redo-ifchange genfile1
-
-# but genfile2.do was gone last time, so genfile2 no longer depends on it.
-# thus, it can be considered up-to-date.  Prior versions of redo had a bug
-# where the dependency on genfile2.do was never dropped.
-../flush-cache
-redo-ifchange genfile1
-
-COUNT=$(wc -l <genfile.log)
-. ../skip-if-minimal-do.sh
-[ "$COUNT" -eq 2 ] || exit 77