test and fix for LOGSTASH-2288
Remove the ability to run multiple commands

Addresses #1747.
This removes the argument list iteration and spawning of multiple
tasks.
It's still possible to specify aditional arguments but now they're
ignored.

PR: #1752
spec the absense and wrong commands

PR: #1752
stringify all symbols in twitter hash


Fixes #1450
add robustness to tweets stream handling


Fixes #1450
monkey patch twitter gem to trap json parsing exceptions and use our own json parser


Fixes #1450
support :symbolize_keys options for json parsing


Fixes #1450
honor common to_json method signature


Fixes #1772
add ruby filter spec


Fixes #1772
Updated link in syslog documentation


Fixes #1724
specify ctrl-d to halt pipeline


Fixes #1767
CTRL-C Enter is OK too


Fixes #1767
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  CTRL-C Enter is OK too
  specify ctrl-d to halt pipeline
  Updated link in syslog documentation
  add ruby filter spec
  honor common to_json method signature
  support :symbolize_keys options for json parsing
  monkey patch twitter gem to trap json parsing exceptions and use our own json parser
  add robustness to tweets stream handling
  stringify all symbols in twitter hash
  spec the absense and wrong commands
  Remove the ability to run multiple commands
  test and fix for LOGSTASH-2288

Conflicts:
	lib/logstash/config/config_ast.rb