#27 Client UserTransaction support

[Ole Husgaard]

Added UserTransaction support for stand-alone clients.

This implementation is suitable for thin clients, as it
offloads all transaction handling to the server, using
RMI communication.
It is completely independent of the underlying JTA
implementation used.

This is a very special use of transaction context
propagation: Nothing in the client will run under
transactions started by the client UserTransaction, but
everything at the server will.