Fix big thread concurency mistake in ZMySQLDA/db.py: the object registerable to transaction manager was the one chared by all threads, preventing multiple threads from effectively registering to transaction manager. This caused MySQL deadlocks, since commits were never issued in all concurent threads but one. This patch creates a new intermediate object between DB and DA which just handles pooling - and factorising connection string parsing and server capabilities probing.
Update DA so it uses the intermediate class.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@13846 20353a03-c40f-0410-a6d1-a30d3c3de9de