routine, which correctly recognises the Gaussian kernel as a separable
    filter. As a result, it is now 50% faster because the normalisation
    occurs at kernel build time.

git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@2661 92316355-f0b4-4df1-b90c-862c8a59935f