top level filter not resulting in an actual filter is ignored
when parsing a filter, we use null to indicate that this filter should not match anything, the top level filter doesn't take it into account
fixes #3356
introduce read/writeSharedString while streaming
currently, we treat all strings as shared (either by full equality or identity equality), while almost all times we know if they should be serialized as shared or not. Add an explicitly write/readSharedString, and use it where applicable, and all other write/readString will not treat them as shared
relates to #3322
Fix ConcurrentPercolatorTests that failed occasionally when running with other tests, by not using the shared test cluster.
Use systemd configuration file for applying limits correctly

In case systemd is used, ulimit is not called (as it would be in the initscript)
and has to be configured in the systemd configuration.

For more information about the parameters LimitNOFILE and LimitMEMLOCK
see http://www.freedesktop.org/software/systemd/man/systemd.exec.html
pattern replace with empty "" setting fails
we should default the replacement to "", since in the settings, if its set to "", we remove the setting
Added percolate statistics to indices and node stats.

Relates to #3173
Be consistent with the default value of `acceptable_overhead_ratio`.
fix percolate stats tests failures
Zen Discovery Cluster Events to have Priority.URGENT
Master node cluster state events resulting in zen discovery (node gets added, removed, for example) should be processed with priority URGENT as its always better to process them as fast as possible, and not let other events get in the way.
closes #3361
reroute post shard started should have HIGH prio as well
Test to some extent the time spent on percolating.
add ability to associate a timeout with a priority executor
enhancement that can be used later to timeout tasks that are pending, also added the ability to get the pending task list from the executor
Transport: Add a dedicated ping channel
Today, we have a low/med/high channel groups in our transport layer. High is used to publish cluster state and send ping requests. Sometimes, the overhead of publishing large cluster states can interfere with ping requests.

Introduce a new, dedicated ping channel (with size 1) to have a channel that only handles ping requests.
closes #3362
catch failures and notify the listener in aliases action handling
Fix ConcurrentPercolatorTests replaces CountDownLatches array by a Semaphore.

The writes to the CountDownLatches array wasn't visible by all threads when the countdown latch array slots were re-initialized.
Cut over to JUnit & Randomized Runner from TestNG

For better integration with the Lucene Test Framework and the
availabilty of RandomizedRunner / Randommized Testing this commit
moves over from TestNG to JUnit.
This commit also moves relevant places over to RandomzedRunner for
reproduceability and removes copied classes from the Lucene Test
Framework.
next iter
iteration :)