Fix local_to event (#46)

Some events not only have `to` but also `orig_to`.

Author: widhalmt

filter-50-local.conf

@@ -1,7 +1,7 @@
 filter {
   if [postfix][component] == "local" {
     grok {
-      match => ["message","to=<%{DATA:[destination][user][email]}>, relay=%{HOSTNAME:[postfix][relay]}, delay=%{NUMBER:[postfix][delay]:float}, delays=%{DATA:[postfix][delays]}, dsn=%{DATA:[postfix][dsn]}, status=%{WORD:[postfix][status]} \(%{GREEDYDATA:[postfix][detail]}\)"]
+      match => ["message","to=<%{DATA:[destination][user][email]}>(, orig_to=<%{DATA:[postfix][orig_to]}>)?, relay=%{HOSTNAME:[postfix][relay]}, delay=%{NUMBER:[postfix][delay]:float}, delays=%{DATA:[postfix][delays]}, dsn=%{DATA:[postfix][dsn]}, status=%{WORD:[postfix][status]} \(%{GREEDYDATA:[postfix][detail]}\)"]
       id => "postfix_local"
       tag_on_failure => ["_grokparsefailure","postfix_local_failed"]
       add_field => {