Test for the previous bugfix.

This fails if you make test *twice* without the preceding patch.
Unfortunately I couldn't find a good way to make it fail if you only make
test once.

t/deps/test1.do

@@ -0,0 +1,14 @@
+# force-rebuild t1dep
+redo t1dep
+
+if [ -e t1a ]; then
+	BEFORE="$(cat t1a)"
+else
+	BEFORE=
+fi
+redo-ifchange t1a  # it definitely had to rebuild because t1dep changed
+AFTER="$(cat t1a)"
+if [ "$BEFORE" == "$AFTER" ]; then
+	echo "t1a was not rebuilt!" >&2
+	exit 43
+fi