add var_append.mk

--- out.make    2015-04-02 16:09:16.418636676 +0900
+++ out.kati    2015-04-02 16:09:16.418636676 +0900
@@ -1,10 +1,10 @@
 === test ===
 echo "simple FOO "
 simple FOO
-echo "recursive FOO BAR"
-recursive FOO BAR
-echo "simple"
-simple
+echo "recursive FOO "
+recursive FOO
+echo "recursive"
+recursive
 echo "recursive"
 recursive
1 file changed