perf scripts python: Give field dict to unhandled callback

trace_unhandled() callback does not allow to access event fields, this patch
resolves the problem.

It can also been used as a more pythonic and flexible way for script writters
to demux event types

This will for example greatly simplify pytimechart event demux.

Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Tom Zanussi <tzanussi@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>,
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <1275340329-2397-1-git-send-email-tardyp@gmail.com>
Signed-off-by: Pierre Tardy <tardyp@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>