Patch logstash server to handle nested event structures

The lumberjack gem does not handle nested fields on import.  If a nested field is sent, "[a][b]", it gets flattened to "a.b".  This patch fixes the problem by splitting the field names on the embedded '.' and nesting the results.  There are probably better ways to write the Ruby, but I'm a beginner at Ruby.

This is [Logstash-1603](https://logstash.jira.com/browse/LOGSTASH-1603).