Add a redo-ifcreate test.

Turns out we weren't testing this one at all, which is a shame, because it
totally didn't work.

t/ifcreate-test.do

@@ -0,0 +1,21 @@
+rm -f exists ifcreate[12] ifcreate[12].log ifcreate[12].dep
+. ./skip-if-minimal-do.sh
+touch exists
+redo-ifcreate exists 2>/dev/null && exit 91
+rm exists
+redo-ifcreate exists || exit 92
+
+for d in 1 2; do
+	redo ifcreate$d
+	[ "$(wc -l <ifcreate$d.log)" -eq 1 ] || exit ${d}1
+	redo-ifchange ifcreate$d
+	[ "$(wc -l <ifcreate$d.log)" -eq 1 ] || exit ${d}2
+	./flush-cache.sh
+	touch ifcreate$d.dep
+	redo-ifchange ifcreate$d
+	[ "$(wc -l <ifcreate$d.log)" -eq 2 ] || exit ${d}3
+	./flush-cache.sh
+	rm ifcreate$d.dep
+	redo-ifchange ifcreate$d
+	[ "$(wc -l <ifcreate$d.log)" -eq 3 ] || exit ${d}4
+done