Support for default.*.do rules.

I *think* this was the last missing part from djb's spec.  Certainly it's an
important one for any real project.

t/.gitignore

@@ -0,0 +1,6 @@
+c
+c.c
+c.c.c
+c.c.c.b
+c.c.c.b.b
+d

t/all.do

@@ -1,2 +1,2 @@
-redo-ifchange hello yellow bellow
+redo-ifchange hello yellow bellow c d
 

t/c.c.c.b.b.a

@@ -0,0 +1 @@
+chicken

t/c.do

@@ -0,0 +1,3 @@
+redo-ifchange $1$2.c
+echo c.do
+cat $1$2.c

t/clean.do

@@ -0,0 +1,3 @@
+rm -f c c.c c.c.c c.c.c.b c.c.c.b.b d
+
+

t/default.b.do

@@ -0,0 +1,10 @@
+if [ -e "$1$2.a" -o -e "default$2.a" ]; then
+	redo-ifchange "$1$2.a"
+	echo a-to-b
+	cat "$1$2.a"
+else
+	redo-ifchange "$1$2.b"
+	echo b-to-b
+	cat "$1$2.b"
+fi
+./sleep 1.1

t/default.c.c.do

@@ -0,0 +1,4 @@
+redo-ifchange $1$2.b
+echo b-to-cc
+cat $1$2.b
+./sleep 1.2

t/default.c.do

@@ -0,0 +1,4 @@
+redo-ifchange $1$2.c
+echo c-to-c
+cat $1$2.c
+./sleep 1.3

t/default.do

@@ -0,0 +1,4 @@
+redo-ifchange c
+echo default-rule
+cat c
+./sleep 1.4