Repair slot signature typing for "__richcmp__" special method after adding...

Repair slot signature typing for "__richcmp__" special method after adding synthesis from "__eq__" etc. methods.
Add test for "__richcmp__" override of existing "__eq__" etc. methods.

Cython/Compiler/TypeSlots.py

@@ -402,9 +402,9 @@ class SyntheticSlot(InternalMethodSlot):
             return self.default_value
 
 
-class RichcmpSlot(SlotDescriptor):
+class RichcmpSlot(MethodSlot):
     def slot_code(self, scope):
-        entry = scope.lookup_here("__richcmp__")
+        entry = scope.lookup_here(self.method_name)
         if entry and entry.func_cname:
             return entry.func_cname
         elif scope.defines_any(richcmp_special_methods):
@@ -836,7 +836,7 @@ slot_table = (
     GCDependentSlot("tp_traverse"),
     GCClearReferencesSlot("tp_clear"),
 
-    RichcmpSlot("tp_richcompare", inherited=False),  # Py3 checks for __hash__
+    RichcmpSlot(richcmpfunc, "tp_richcompare", "__richcmp__", inherited=False),  # Py3 checks for __hash__
 
     EmptySlot("tp_weaklistoffset"),
 

tests/run/ext_auto_richcmp.py

@@ -216,6 +216,31 @@ class ClassEqNeGe(ClassEqNe):
         return NotImplemented
 
 
+@cython.cclass
+class ClassRichcmpOverride(ClassEqNeGe):
+    """
+    >>> a = ClassRichcmpOverride(1)
+    >>> b = ClassRichcmpOverride(1)
+
+    >>> a == a
+    True
+    >>> a != a
+    False
+
+    >>> a != b if compiled else a == b  # Python ignores __richcmp__()
+    True
+    >>> a == b if compiled else a != b  # Python ignores __richcmp__()
+    False
+
+    >>> if IS_PY2 or not compiled: raise TypeError  # doctest: +ELLIPSIS
+    ... else: a >= b  # should no longer work when __richcmp__ is overwritten
+    Traceback (most recent call last):
+    TypeError...
+    """
+    def __richcmp__(self, other, op):
+        return NotImplemented
+
+
 @cython.cclass
 class ClassLe(X):
     """