Add a fadein test

This also serves as a proof of concept of the screen capture
functionality and as a demo for snapshot-based rendering verification.

Signed-off-by: Bryce Harrington <bryce@osg.samsung.com>
Add test reference directory and images for fadein
tests: Add support for comparing output against reference images

This lift's files_equal() routine to do byte comparison of the rendered
files.  Note that since the clock time will change run to run we can
only compare against the first frame (which will be black).