include debug information in the autoremove-kernels file

Figuring out after the fact what went wrong in the kernel hook is kinda
hart, also as the bugreports are usually very lacking on the details
front. Collecting the internal variables in the debug output we attach
to the generated file might help shine some light on the matter.
It's at least not going to hurt…

debian/apt.auto-removal.sh

@@ -47,13 +47,33 @@ generateconfig() {
 APT::NeverAutoRemove
 {
 EOF
-	apt-config dump --no-empty --format '%v%n' 'APT::VersionedKernelPackages' | while read package; do
+	for package in $(apt-config dump --no-empty --format '%v%n' 'APT::VersionedKernelPackages'); do
 		for kernel in $kernels; do
 			echo "   \"^${package}-${kernel}$\";"
 		done
 	done
 	echo '};'
+	if [ "${APT_AUTO_REMOVAL_KERNELS_DEBUG:-true}" = 'true' ]; then
+		cat <<EOF
+/* Debug information:
+# dpkg list:
+$(dpkg -l | grep '\(linux\|kfreebsd\|gnumach\)-image-')
+# list of installed kernel packages:
+$list
+# list of different kernel versions:
+$debverlist
+# Installing kernel: $installed_version ($1)
+# Running kernel: $running_version ($unamer)
+# Last kernel: $latest_version
+# Previous kernel: $previous_version
+# Kernel versions list to keep:
+$debkernels
+# Kernel packages (version part) to protect:
+$kernels
+*/
+EOF
+	fi
 }
-generateconfig > "${config_file}.dpkg-new"
-mv "${config_file}.dpkg-new" "$config_file"
+generateconfig "$@" > "${config_file}.dpkg-new"
+mv -f "${config_file}.dpkg-new" "$config_file"
 chmod 444 "$config_file"