Data structure seems appropriate as from a master point of view, a client
can initiate more than on transaction at time (as it's multithreaded) so
it is required to index current transaction by UUID first, then by tid.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@1729 71dcc9de-d417-0410-9af5-da40c76e7ee4