Thanks for the quick fix ! Unfortunately in the new postinst and postrm files you typed something with "xen?-linux" in your regexp and it doesn't match the new value of kimage (xen0-linux in my case). I guess "xen[0u]-linux" would do the trick.
By the way you could also change the package_name variable in those files to reflect the new package name (even if the current situation doesn't seem harmful). Right know it's still equal to "linux-image...". -- Jean-Pierre Flori