initial support for multiple video tracks
modified GPUImageMovie to support transitions (not at all tested)
more support for reading multiple movie tracks
keep track of each tracks "done reading" state
only send the later, valid timestamp through
update transitions on every frame
removed extraneous method declarations
push whichever timestamp is incoming
2nd input to two input filter can also set size
GPUImageMovie outputs frames in the correct order
better handling of asset reading failure
stop lying to video overlay
renamed LinkedOverlayDelegate to LinkedOverlay