add sort filter
filters: date: add target option

Update the date filter to support a target option.  If defined,
instead of updating the @timestamp field, update the given target field.
This is useful for events that have multiple timestamps (e.g., start and
end times).
- Check for EOF condition (remote has closed) before writing.

If we don't do this, then the write will still succeed even after the
remote has closed (half-closed in CLOSE_WAIT on our side), and the 2nd
write after will fail causing the previous event to be lost.
- Try forever to connect w/ exponential backoff
- remove a blank line
remove old event shims and fix any uses of it
remove commented code
add test case, found some issue and fixed them.
Allow empty plugin sections again.

This used to work with 1.1.x.

See: https://logstash.jira.com/browse/LOGSTASH-1344
Merge pull request #664 from bernd/LOGSTASH-1344

Allow empty plugin sections again (LOGSTASH-1344)
Merge pull request #625 from jdve/date-overwrite

filters: date: add target option
1) adjust the comments
2) change milestone to 1
3) add comments for the ignored case.
Merge pull request #609 from fbird/master

add sort filter
add coverage
Update walkthrough conf files to reflect 1.2.x syntax changes
make comment clearer
Merge pull request #667 from logstash/doc-fix

Update walkthrough conf files to reflect 1.2.x syntax changes
don't let travis build jars
fetch geoip DB before tests
Merge branch 'filter-tests' into travis