Added srg0004: a simple left-recursive grammar.

test/srg/srg0004/lr.gf

@@ -0,0 +1,7 @@
+cat S;
+
+fun f : S -> S ; 
+    g : S ;
+
+lin f x = { s = x.s ++ "f" } ;
+    g = { s = "s" } ;