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.
template-match must wait for a change, while the single frame mode is
either wait or next. The default value was correct, but using an unrelated
constant.
A new property `singleFrameMode` has been added to motiondetect, that
behaves exactly the same way as in detect-match.
A loop has been added in template-match to check that the property
singleFrame was actually changed when exiting g_cond_wait.

Added synchronization fix in the "get property" function and signalling
when the gstreamer element itself modifies its attribute.
Added the timestamps difference to the failure message.