Add a test for the preceding fix (nonexistent directories).

t/autosubdir/clean.do

@@ -0,0 +1,2 @@
+rm -rf *.tmp
+rm -f *~ .*~

t/autosubdir/default.txt.do

@@ -0,0 +1,2 @@
+mkdir -p $(dirname $1)
+echo "hello" >$3

t/autosubdir/test.do

@@ -0,0 +1,3 @@
+rm -rf sub.tmp
+redo-ifchange sub.tmp/test.txt
+[ -e sub.tmp/test.txt ] || exit 96