Fix problem in MONTHNUM and add DATESTAMP_EVENTLOG pattern and 

Whilst trying to get Windows Event Log data into logstash I had some problems with the the timestamp format Windows uses.

Taking an example value (the TimeGenerated field provided by the eventlog input):

20131218141650.687853-000

And using:

%{YEAR}%{MONTHNUM}%{MONTHDAY}%{HOUR}%{MINUTE}%{SECOND}

I get a %{MONTHNUM} value of 1, but it should be 12. This is because the MONTHNUM pattern allows for single digit month values. I created a new pattern which removed this flexibility:

MONTHNUM2 (?:0[1-9]|1[0-2])

This, along with the pattern below works as I would expect:

DATESTAMP_EVENTLOG %{YEAR}%{MONTHNUM2}%{MONTHDAY}%{HOUR}%{MINUTE}%{SECOND}

I'm sure there's a better way of implementing this but I think this is a genuine problem.
Moved 'success' message into the begin block so it doesn't get printed if there's an error
Fixes exception when not specifying yamlmibdir

Fixes 'undefined method `empty?` for nil:NilClass exception
Add a RFC2822 compliant date pattern

The pattern is defined in RFC2822 and differs from the one defined in
RFC822:
 http://www.ietf.org/rfc/rfc2822.txt

Example:
 Mon, 20 Jan 2014 18:40:18 +0100
on broken pipes - ie program exit, EBADF can will be used instead of EPIPE. This commit will allow pipe command to be restarted.
Update java

Added support for an "_" in the JAVACLASS and added support for a space in the JAVAFILE expression.

Examples are: "at org.jnp.server.NamingServer_Stub.lookup(Unknown Source)"

This example would have failed without the update.
Add some patterns I found useful in parsing mongo logs.
Fix syntax errors in kv examples

Fix syntax errors in examples for the include_keys, exclude_keys and default_keys config values.
Prefix patterns with MONGO_
Merge pull request #1109 from ronnocol/master

FIX for 1931: plugin script doesn't complete
Merge pull request #1111 from ronnocol/master

Close LOGSTASH-1933:
Merge remote-tracking branch 'upstream/master'
Merge pull request #1112 from ronnocol/master

Fix LOGSTASH-1936
Fix for LOGSTASH-1920
Remove path from `pwd`
I yield.  Going with `unset CDPATH`.  May the odd user this affects forgive me now.
Only abort on 'embedded => true' if we are *NOT* JRuby.

As it turns out, programming is this terrible journey where we have
humans using some kind of silly error prone process whereby intent of
function is converted to instructions.

I am bad at programming sometimes.
Merge pull request #1113 from untergeek/untergeek-binfix

Fix for LOGSTASH-1920
log files path into /tmp, added missing mutate + replace statements
awesome description