Allow a "*count" suffix in a screen line to repeat the screen line for
"count" times.
The change is made to Screen:expect() and Screen:get_snapshot() instead
of Screen:render() so that screen expectations generated using code can
still work and test failures can still be readable.
A snapshot is now also printed on failure so that there is no need to
run the test again with Screen:snapshot_util().
c2249f6abf