Spec for HAPROXYHTTP pattern.

We ran into parsing problems with this pattern and my first step was to
look at the tests. There were none so I took the apache log example and
adapted it for haproxy using the haproxy documentation format as the
example log string.

HELP! I am not sure why using date { timestamp =>
"dd/MMM/YYYY:HH:mm:ss.S" } doesn't set the event timestamp correctly so
the example uses mutate but at least passes.
Use date filter to set the timestamp from the haproxy accept_date
Remove date filter from haproxy parsing example.
LOGSTASH-1106 Adding additional file output path option documentation. This is to highlight functionality of the path option that was not previously documented, and to prevent additional pull requests for implementation of date-based log rotation.
Add missing changelog for version 1.1.13.
Merge pull request #500 from bernd/changelog-update-1.1.13

Add missing changelog for version 1.1.13
ruby filter: multi-instance support
Merge pull request #501 from nikicat/fix-ruby-filter

ruby filter: multi-instance support
- try to fix prune specs, but I think there are actually bugs found by
  the tests that need fixing now.
- fix range filter specs
- fix split filter specs
- fix translate filter specs
- default useragent filter to target the root of the event instead of
  writing into the "ua" field.
- fix useragent specs
- fix xml specs
Fix another json spec failure (typo)
- fix alter filter specs
- fix failling clone filter spec (Event#clone wasn't a deep enough copy)
- fix multiline specs
- added 'source' setting to multiline filter now that there's no
required "@message" field (due to event v1 schema)
Disable the 'prune' filter spec because the test should have always failed, but it didn't, and I'm not sure what to do next...