changed teh way single images operate,
* they dont act like a sequence of 1 image - so you can drag and resize without the trouble of having teh center image.
* they draw without the single frame in them. and no 'gutter?' strip drawing.
* the start frame is always set to be where the handles start.
This is done in the transform and draw areas of the sequencer. added 2 functions,
fix_single_image_seq - moves the seq start without any visible change - so it will load in older blend's
check_single_image_seq - quick way to check for single image.
80af4ce69d