Better 3.7 CALL_METHOD_KW handling

- Handles positional args now

test/simple_source/bug_pypy37/01_callback.py

@@ -1,10 +1,21 @@
 """This program is self-checking!"""
 
 
+class C:
+    def sort(self, l, reverse, key_fn):
+        # PyPy example of CALL_METHOD_KW 2
+        # 2 keyword arguments and no positional arguments
+        return l.sort(reverse=reverse, key=key_fn)
+
+
 def lcase(s):
     return s.lower()
 
 
+x = C()
 l = ["xyz", "ABC"]
-l.sort(key=lcase)
+
+# Another PyPy example of CALL_METHOD_KW 2
+# 2 keyword arguments and one positional argument
+x.sort(l, reverse=False, key_fn=lcase)
 assert l == ["ABC", "xyz"]