- upgrade jruby
Make event specs pass under event_v1

This required implementing Event#append. Some semantics have changed.
"@message" and "@tags" are no longer handled specially (mainly because
they aren't described by event v1 schema). This likely has broken the
multiline filter tests (intentionally). The multiline filter will need
to have custom merging of certain fields (like joining message with
newlines instead of putting it all in an array)
- all event tests now passing with event v1
- make event v1 the default.
- grok tests now pass under event v1
- Added 'overwrite' setting to allow %{FOO:message} to overwite
  'message' field (or any other field.
Update changelog
- date filter specs now passing against event v1
- fix date perf test (which runs 30% faster than logstash v1.1.12)
style
- make mutate specs pass in event v1
- skip missing fields (avoids crashing)
- make anonymize specs pass under event v1
Merge git://github.com/logstash/logstash