Work around mutex lock in geoip ruby module. Doing it this way consumes slightly more memory but unblocks the threads when there is a high amount of concurrency against geoip lookups (eg, when you are processing web server logs).
Merge pull request #990 from avleen/geoip_mutex

Work around mutex lock in geoip ruby module. This measurably helps performance by avoiding locking when using multiple filter workers. Every copy of a geoip filter in each filter worker now gets a thread-local GeoIP handle.
Merge git://github.com/logstash/logstash