create(options=>{}) not working as expected

[gwynp]

I was expecting that if had 
        POE::Session->create(
                ....
                options=>{trace=>0},
                ....
        );

then tracing would be OFF.  This seems to not be the case, because
POE::Session uses exists($self->[SE_OPTIONS]->{OPT_TRACE})!  This doesn't
seem very logical to me.

OPT_TRACE is checked in 3 places : twice in _invoke_state and once in
register_state.

-Philip