Silently substituting the password field was nice, but for mechs
that can use either the password or an access token, it makes
things very difficult. This really only affects MSN clients since
Facebook clients should already be setting the api key.
Based on profiling, using around 35 stream handlers quarters the number
of basic message stanzas that can be processed in a second, in
comparison to only using the bare minimum of four handlers.
To help, we can drop handlers for stream features once the session
has started. So that we can re-enable these handlers when a stream
must restart, the 'stream_start' event has been added which fires
whenever a stream header is received.
The 'stream_start' event is a more generic replacement for the
existing start_stream_handler() method.
Note that using % in a string will _always_ perform the sting substitutions, because the strings are constructed before the function is called. So log.debug('%s' % expensiveoperation()) will take about the same CPU time whether or not the logging level is DEBUG or INFO. if you use , no substitutions are performed unless the string is actually logged
