Log script change/add and removal at INFO level

Closes #6104
Significant_terms agg: added option for a background_filter to define background context for analysis of term frequencies

Closes #5944
[DOCS] Fix typos in context suggest
Use t-digest as a dependency.

Our improvements to t-digest have been pushed upstream and t-digest also got
some additional nice improvements around memory usage and speedups of quantile
estimation. So it makes sense to use it as a dependency now.

This also allows to remove the test dependency on Apache Mahout.

Close #6142
[TEST] Changed the possessive matching syntax in cat.recovery
regex to use an independent subexpression. Possessive
modifiers not supported on older Perl
[DOCS] Changed coming[1.1.0] to added in snapshot status
[JAVADOCS] Fix wrong javadoc in IdentityHashSet.

Close #6121
[TEST] Ensure no bechmarks are running after test
Report all errors if benchmark fails and mark as failed
Log cache recycler clear call as debug
Read full message on free context

Since #5730 we write a boolean in the FreeContextResponse which should be deserialized

Closes #6147
Fix NPE when initializing an accepted socket in NettyTransport.

NettyTransport's ChannelPipelineFactory uses the instance variable
serverOpenChannels in order to create sockets. However, this instance variable
is set to null when stoping the netty transport, so if the transport tries to
stop and to initialize a socket at the same time you might hit the following
NullPointerException:

[2014-05-13 07:33:47,616][WARN ][netty.channel.socket.nio.AbstractNioSelector] Failed to initialize an accepted socket.
java.lang.NullPointerException: handler
	at org.jboss.netty.channel.DefaultChannelPipeline$DefaultChannelHandlerContext.<init>(DefaultChannelPipeline.java:725)
	at org.jboss.netty.channel.DefaultChannelPipeline.init(DefaultChannelPipeline.java:667)
	at org.jboss.netty.channel.DefaultChannelPipeline.addLast(DefaultChannelPipeline.java:96)
	at org.elasticsearch.transport.netty.NettyTransport$2.getPipeline(NettyTransport.java:327)
	at org.jboss.netty.channel.socket.nio.NioServerBoss.registerAcceptedChannel(NioServerBoss.java:134)
	at org.jboss.netty.channel.socket.nio.NioServerBoss.process(NioServerBoss.java:104)
	at org.jboss.netty.channel.socket.nio.AbstractNioSelector.run(AbstractNioSelector.java:318)
	at org.jboss.netty.channel.socket.nio.NioServerBoss.run(NioServerBoss.java:42)
	at org.jboss.netty.util.ThreadRenamingRunnable.run(ThreadRenamingRunnable.java:108)
	at org.jboss.netty.util.internal.DeadLockProofWorker$1.run(DeadLockProofWorker.java:42)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:745)

This fix ensures that the ChannelPipelineFactory always uses the channels that
have been used upon start, even if a stop request is issued concurrently.

Close #6144
Removed useless and illegal json object in the response.

Relates to #5865
Clarify `missing` behavior.
Update repositories.asciidoc
Improved instructions for using YUM