Added option to composite/viewer nodes which specifys whether alpha input
is straight or not (premultiplied is default).

This is useful in cases when you want to check on output of such nodes
as keying which does have straight alpha output.

Also added missing do_version code to previous compo do_versions.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54429 954f8c5b-7b00-dc11-b283-0030488c597c