Refactored code in MessageIterator. It needs to know if the current mode is
"leky" or "non-leaky", so "_process_all_frames has been set as a global
variable.
In order to avoid using a video file `timer.mpg`, the unit test
`test_match_consecutive_timed_frames` now looks for the milliseconds and
checks that the frames where there were matches are consecutive by looking
at their timestamps.