--- Blender version with error, and version that worked ---

The current ones from builder.blender, with example I'm now with 54335.. It was working fine the last official version.

--- Short description of error ---

Well before, while at the compositing process, each layer automatically has an alpha channel, with which the sky part is made transparent, so to composite a cube on top of my input I would only alpha over it without having to worry about anything else... but now If I would to render anything and be willing to use its alpha channel, I no longer have it by default, but instead I should go to the layer settings and turn off the sky, and the button order to chose which channels to display is now different in both image editor and compositor, It starts with alpha and colors and then colors... I highly doubt that to be a new intended behavior, because It's just frustrating, and might lead one to re-render in case he wanted the sky back...

--- Steps for others to reproduce the error (preferably based on attached .blend file) ---

render the default scene, and try to save it with an alpha channel...