dpkg-maintscript-helper: Accept multiple arguments in error and warning

This allows to split overly long strings into smaller chunks on multiple
lines.

scripts/dpkg-maintscript-helper.sh

@@ -247,12 +247,12 @@ debug() {
 }
 
 error() {
-	echo "$PROGNAME: error: $1" >&2
+	echo "$PROGNAME: error: $*" >&2
 	exit 1
 }
 
 warning() {
-	echo "$PROGNAME: warning: $1" >&2
+	echo "$PROGNAME: warning: $*" >&2
 }
 
 usage() {