Use first parameter as backup_suffix if backup_suffix is unset or empty

maint/ldiff

@@ -3,7 +3,7 @@
 # This script makes pretty looking patches provided that the old files
 # are kept around with the .v0 suffix.
 
-: ${backup_suffix="\.v0"}
+: ${backup_suffix=${1:-"\.v0"}}
 backup_files=`find . -path "*$backup_suffix" -type f | sort -u`
 for oldfile in $backup_files; do
   newfile=`echo $oldfile | sed 's,^\./,,;s/'$backup_suffix'$//'`