Match ZODB commit 69c18075dafca12a7bb4d431751d40c2f0f2884e.

ClientStorage.py can deadlock in tpc_begin

Correct potential deadlock in ClientStorage:tpc_begin by being sure to release locks in a finally block.

we don't run tests for transaction here either.

Preparation for kliling the last ZODB-dependent test in the standalone
'persistent' package.

Put them inside ZODB/tests in anticipation of separating persistent from
ZODB.

Use instead the decorator ('zope.interface.implementer').

https://bugs.launchpad.net/zodb/+bug/993350

  can discover addresses when dynamic port assignment (bind to port 0)
  is used. This could, for example, be used to update address
  information in a ZooKeeper database.

- Client storagers have a method, new_addr, that can be used to change
  the server address(es). This can be used, for example, to update a
  dynamically determined server address from information in a
  ZooKeeper database.

- Moved some responsibility from runzeo to StorageServer to make it
  easier to use storage servers without runzeo.

  Conflict resolution failed when state included persistent references
  (local or cross-database) with classes that couldn't be imported.