Add a new passfailtest.

This tests that the target file isn't removed or changed if building fails.

t/.gitignore

@@ -6,3 +6,4 @@ c.c.c.b.b
 d
 test.args
 test2.args
+/passfail

t/passfail.do

@@ -0,0 +1,6 @@
+echo $$
+if [ -e pleasefail ]; then
+	exit 1
+else
+	exit 0
+fi

t/passfailtest.do

@@ -0,0 +1,28 @@
+rm -f pleasefail
+redo passfail
+if [ ! -e passfail ]; then
+	echo "passfail should exist" >&2
+	exit 42
+fi
+PF1=$(cat passfail)
+touch pleasefail
+if redo passfail 2>/dev/null; then
+	echo "redo passfail should have failed" >&2
+	exit 42
+fi
+if [ ! -e passfail ]; then
+	echo "passfail should STILL exist" >&2
+	exit 42
+fi
+PF2=$(cat passfail)
+if [ "$PF1" != "$PF2" ]; then
+	echo "passfail changed even though it failed" >&2
+	exit 42
+fi
+rm -f pleasefail
+redo passfail || exit 43
+PF3=$(cat passfail)
+if [ "$PF1" = "$PF3" ]; then
+	echo "passfail did not change even though it passed" >&2
+	exit 42
+fi

t/test.do

@@ -1,4 +1,4 @@
 redo-ifchange all
 ./hello >&2
-redo deltest deltest2 test.args test2.args curse/test deps/test
+redo deltest deltest2 test.args test2.args passfailtest curse/test deps/test