Fix 3.2 for/if loopback bug

problem was handling in Python 3.2

 for ...
    if ...
    else:
      ....
      jump for
    come from if
    jump for

In later Python 3's a "come from" is removed.

Also, start to DRY parser{,2,3} grammar rules.

test/simple_source/looping/10_for_if_loopback.py

@@ -0,0 +1,23 @@
+# In Python 3.2 JUMP_ABSOLUTE's (which can
+# turn into COME_FROM's) are not optimized as
+# they are in later Python's.
+#
+# So an if statement can jump to the end of a for loop
+# which in turn jump's back to the beginning of that loop.
+#
+# Should handle in Python 3.2
+#
+#          98	JUMP_BACK         '16' statement after: names.append(name) to loop head
+#       101_0	COME_FROM         '50' statement: if name == ...to fictional "end if"
+#         101	JUMP_BACK         '16' jump as before to loop head
+
+def _slotnames(cls):
+    names = []
+    for c in cls.__mro__:
+        if "__slots__" in c.__dict__:
+            slots = c.__dict__['__slots__']
+            for name in slots:
+                if name == "__dict__":
+                    continue
+                else:
+                    names.append(name) # 3.2 bug here jumping to outer for