Fixed ``testZODBCompat`` tests in ZopeTestCase to match modern ZODB semantics. There is no explicit contract for the time _v attributes actually get removed. The tests in question where bogus, as they didn't test database load but a class variable not affected by the transaction machinery. There's other tests in the same module testing more abort semantics that have a proper demo storage setup.

Updated to zope.testbrowser = 3.10.1 and make sure we keep the new mechanize, even though it will be downgraded in ZTK 1.0c2 to support Python 2.4