Fixed a verifyClass false positive with a decorated method.

This bug was a reason (?) for a gratuitous fork of the _verify
function in z3c.testing.verify.

src/zope/interface/tests/test_verify.py

@@ -491,6 +491,29 @@ class Current:
 
         self._callFUT(ICurrent, Current)
 
+
+    def test_w_decorated_method(self):
+        from zope.interface import Interface
+        from zope.interface import implementer
+
+        def decorator(func):
+            # this is, in fact, zope.proxy.non_overridable
+            return property(lambda self: func.__get__(self))
+
+        class ICurrent(Interface):
+
+            def method(a):
+                pass
+
+        @implementer(ICurrent)
+        class Current(object):
+
+            @decorator
+            def method(self, a):
+                pass
+
+        self._callFUT(ICurrent, Current)
+
 class Test_verifyObject(Test_verifyClass):
 
     def _callFUT(self, iface, target):

src/zope/interface/verify.py

@@ -76,6 +76,10 @@ def _verify(iface, candidate, tentative=0, vtype=None):
         elif (isinstance(attr, MethodTypes)
               and type(attr.__func__) is FunctionType):
             meth = fromMethod(attr, iface, name)
+        elif isinstance(attr, property) and vtype == 'c':
+            # We without an instance we cannot be sure it's not a
+            # callable.
+            continue
         else:
             if not callable(attr):
                 raise BrokenMethodImplementation(name, "Not a method")