Use resource warning messages to notify camerabin2 that a capture
as aborted or couldn't be started, making it decrement the
processing counter and making the idle property more reliable.
Checks if the new received preview-caps are equal to what is
already in use, skips the preview-caps setting logic in case
new caps are same as current ones.
Adds a virtual function to basecamerasrc in case subclasses want to be
notified of changing preview caps. This is useful if the subclass wants
to post the preview itself or if it wants to provide a preview buffer
as close to as possible to the user's requested resolution to the
preview generation pipeline.
Adds some more logging and always assume capture has started before
start_capture is called. This helps on image captures that might
call finish_capture directly from start_capture or before start_capture
finishes.
