add another simple function test

test/cases/function_definition/function_foo2.tst

@@ -0,0 +1,22 @@
+int foo(int x)
+  int a = 5
+  return a
+end
+3.foo( 4 )
+-- -- --
+s(:expressions,
+  s(:function, :int,
+    s(:name, :foo),
+    s(:parameters,
+      s(:parameter, :int, :x)),
+    s(:expressions,
+      s(:field_def, :int, :a,
+        s(:int, 5)),
+      s(:return,
+        s(:name, :a)))),
+  s(:call,
+    s(:name, :foo),
+    s(:arguments,
+      s(:int, 4)),
+    s(:receiver,
+      s(:int, 3))))