Consider writerIndex when LzfDecoder writes into a new heap buffer

Motivation:

Now LzfDecoder do not consider writerIndex when it writes into array of a new heap buffer (when it decodes a compressed chuck of data)
Add test cases for HttpContentCompressor

- Ported from 386a06dbfa13f981aff59a9abb7cbecee2701e65
Fix a bug where SpdySession.getActiveStreams() returns incorrect set

Related issue: #2743

Motivation:

When there are more than one stream with the same priority, the set
returned by SpdySession.getActiveStream() will not include all of them,
because it uses TreeSet and only compares the priority of streams. If
two different streams have the same priority, one of them will be
discarded by TreeSet.

Modification:

- Rename getActiveStreams() to activeStreams()
- Replace PriorityComparator with StreamComparator

Result:

Two different streams with the same priority are compared correctly.
Fix resource leaks in StompSubframeAggregatorTest
[#2744] Fix flakey HashedWheelTimerTest.testExecutionOnTime()

Motivation:

The calculation of the max wait time for HashedWheelTimerTest.testExecutionOnTime() was wrong and so the test sometimes failed.

Modifications:

Fix the max wait time.

Result:

No more test-failures
ForkJoinPool
Channel Deregistration
Pluggable algorithm to choose next EventLoop

Motivation:

Currently when a new event loop is needed to register a channel our EventLoopGroup implementations just
use a round-robin like algorithm to choose the next event loop. Unfortunately this is not always good
enough as different event loops may become more busy than others over time. This is especially true when
an application handles different kinds of connections (long-living and short-living). This change allows
developers to plug in their own algorithms to choose the next event loop and to collect metrics about the
busyness of the event loops. See #1230

Modifications:

- TODO

Result:

- Developers can plug in their own algorithms into MultithreadEventLoopGroup constructors.
- Developers can gather metrics/feedback from the event loops and use the data in their custom algorithms.

bla