Skip missing fields, as converting those introduces new fields.
Explicitly specify fields to be ignored for GELF.
Add parameter to select the field that provides the GELF short message.
Fix spacing.
Add `short_message` to the list of fields to be ignored for GELF.
Fixed year pattern.

Year was matching any digit, one or more times. This could lead to way
too eager matching.

Match years as either a group of 2, or a group of 4 digits.
Merge pull request #308 from cnf/yearfix

Fixed year pattern.
- fix bad 'source' url (LOGSTASH-821, #306)
- 1.1.8 hasn't been released yet
- report the host/port that is related to EADDRINUSE (LOGSTASH-831)
Update changelog
- version bump
- 1.1.9 dev
Merge branch 'master' of https://github.com/ralphm/logstash into ralphm-master

Conflicts:
	lib/logstash/outputs/gelf.rb
- update changelog for #244
Merge branch 'master' into LOGSTASH-724