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/gentest.do

@@ -0,0 +1,21 @@
+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