There are some problems in the alpha channel support, as is
reported at http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=72917
This patch add a new RCombineAlpha function, based on Gimp. This
function is called when needed in the raster.c functions.
This patch is based on the Brad Jorsch <anomie@users.sourceforge.net>
patch for the 0.62.1-0.1 version.
[crmafra: v1 was sent by Rodolfo kix Garcia <kix@kix.es>]
