tests: check processing of external invalidations by DB/Connection

[jmuchemb]

No description provided.

[jmuchemb]

The failure with FileStorageClientHexTests is due to ZODB:

(Pdb) s
TypeError: 'invalidate() takes exactly 3 arguments (4 given)'
> ZODB/tests/hexstorage.py(107)invalidate()
-> return self.db.invalidate(transaction_id, oids, version)
(Pdb) l
102     
103         def invalidateCache(self):
104             return self.db.invalidateCache()
105     
106         def invalidate(self, transaction_id, oids, version=''):
107  ->         return self.db.invalidate(transaction_id, oids, version)
108     
109         def references(self, record, oids=None):
110             return self.db.references(unhexlify(record[2:]), oids)
111     
112         def transform_record_data(self, data):
(Pdb) self.db
<ZODB.mvccadapter.MVCCAdapter object at 0x7f278969fdd0>