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/example/CC.do

@@ -1,11 +0,0 @@
-redo-ifchange config.sh
-. ./config.sh
-exec >$3
-cat <<-EOF
-	redo-ifchange \$2.c
-	gcc $CFLAGS -MD -MF \$3.deps -o \$3 -c \$2.c
-	read DEPS <\$3.deps
-	rm -f \$3.deps
-	redo-ifchange \${DEPS#*:}
-EOF
-chmod +x $3