The units in the Timeline test suite just rely on the timeline
being a timeout automatically advanced by the main loop. This
is not the case anymore, since the merge of the master-clock.
To make the test units work again we need to "emulate" the master
clock without effectively having a stage to redraw; we do this
by creating a frame source and manually advancing the timelines
we create for test purposes, using the advance_msecs() "protected"
method.
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