During 'NEOCluster.stop', there's often 1 'Serialized.background()' call too
many, and when it removed the last lock of the queue, another thread would hang
if was sleeping between 'q.put(lock)' and 'q.get().release()'.

An easy way to reproduce the bug was to add:
    if cls.pending is None:
        time.sleep(.01)
just before 'q.get().release()'

In particular, this fixes history tab on recent Zope.

Protocol is extended to allow passing None in an Enum field.

Subprocesses should free file descriptors (here a system-wide lock)
they don't need.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2837 71dcc9de-d417-0410-9af5-da40c76e7ee4

This disables commit 4a4d2e64.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2836 71dcc9de-d417-0410-9af5-da40c76e7ee4

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2835 71dcc9de-d417-0410-9af5-da40c76e7ee4

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2834 71dcc9de-d417-0410-9af5-da40c76e7ee4

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2833 71dcc9de-d417-0410-9af5-da40c76e7ee4

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2832 71dcc9de-d417-0410-9af5-da40c76e7ee4

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2831 71dcc9de-d417-0410-9af5-da40c76e7ee4

MySQL connections remained open, which even led to deadlocks with MySQL 5.5

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2830 71dcc9de-d417-0410-9af5-da40c76e7ee4

This makes dropping of partitions very fast, and should also speed up all
other queries to the 'trans', 'obj' & 'obj_short' tables.

However, it is not enabled due to a bug in MySQL 5.1 & 5.5.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2828 71dcc9de-d417-0410-9af5-da40c76e7ee4
git-svn-id: https://svn.erp5.org/repos/neo/trunk@2829 71dcc9de-d417-0410-9af5-da40c76e7ee4

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2827 71dcc9de-d417-0410-9af5-da40c76e7ee4

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2826 71dcc9de-d417-0410-9af5-da40c76e7ee4

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2825 71dcc9de-d417-0410-9af5-da40c76e7ee4

Threaded mode is the fastest so it's the default for neotestrunner.
Speed is not so important for the test bot, so it keeps running them in
functional mode by default.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2824 71dcc9de-d417-0410-9af5-da40c76e7ee4

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2823 71dcc9de-d417-0410-9af5-da40c76e7ee4

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2822 71dcc9de-d417-0410-9af5-da40c76e7ee4

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2821 71dcc9de-d417-0410-9af5-da40c76e7ee4

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2820 71dcc9de-d417-0410-9af5-da40c76e7ee4

It was broken since commit 4a4d2e64
("client: optimize by not calling lastTransaction at the end of transactions").

This fixes several unit tests like
neo.tests.zodb.testBasic.BasicTests.check_tid_ordering_w_commit

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2819 71dcc9de-d417-0410-9af5-da40c76e7ee4