Warn when known bad codecs are used with --sockets.
Warn when known bad codecs are used with --sockets.

Some codecs are geared towards input plugins that naturally emit
discrete messages, like 'stdin' and 'file' which read their input
line by line. Stream-oriented inputs like 'tcp' and 'unix' produce
streams of data and rely on the codec to chop up the stream into
events.

When using the --sockets option you can't use the 'plain' or 'json'
codecs if the test input consists of more than one line. Warn users
about this if they attempt to process testcase file with those codecs
and use the --sockets flag.

Fixes #39.

magnusbaeck/logstash-filter-verifier