[storm] Database disconnection handling

[James Henstridge]

Hi,

I've updated my database disconnect branch, and think it is just about
ready.  The branch is attached to bug 94986, and the branch is at r178
(it looks like Launchpad hasn't yet published the latest changes).

Note that this branch does not impose any retry policy, instead making
it possible to detect the disconnections and then reconnect at the
start of the following transaction.

It is expected that applications would handle disconnections in the
same way as integrity errors or deadlocks.  For example, using Zope's
request retry mechanism.

The tests all pass on my laptop running Gutsy (2.0.6-1ubuntu1),
however I've run into problems testing things interactively related to
http://www.initd.org/tracker/psycopg/ticket/186.  I guess it is a
timing problem.

The branch only includes support for Postgres, but it should be
trivial to support e.g. mysql.  The tests need to be able to connect
to the database via a TCP socket, since it is setting up a simple TCP
proxy to simulate the disconnects.

James.