config grammar: Allow spaces in [field references][like this]

Tests included.

Note about grammar compilation:
  I had to use treetop 1.4.15 (1.5.3 generates ruby code that fails to
  parse, haven't spent any time debugging)

Fixes #1513
Adding delaycompress to logrotate

To avoid issues like:

/etc/cron.daily/logrotate:
gzip: stdin: file size changed while zipping

This change is harmless and will prevent errors like this one
Merge git://github.com/logstash/logstash