Implement cap negotiation 3.2 on server side

Used for "server-dependent" caps which already rely on sending NEW and
DEL to client. This functionality is not yet available for caps added by
modules.

modules/modpython/znc.py

@@ -410,6 +410,9 @@ class Module:
     def OnServerCapAvailable(self, sCap):
         pass
 
+    def OnServerCap302Available(self, sCap, sValue):
+        return self.OnServerCapAvailable(sCap)
+
     def OnServerCapResult(self, sCap, bSuccess):
         pass