Fix buffer leaks in Bzip2DecoderTest
Improve the allocation algorithm in PoolChunk

Motivation:

Depth-first search is not always efficient for buddy allocation.

Modification:

Employ a new faster search algorithm with different memoryMap layout.

Result:

With thread-local cache disabled, we see a lot of performance
improvment, especially when the size of the allocation is as small as
the page size, which had the largest search space previously.
Fix inspector warnings
Optimize PoolChunk

- Using short[] for memoryMap did not improve performance. Reverting
  back to the original dual-byte[] structure in favor of simplicity.
- Optimize allocateRun() which yields small performence improvement
- Use local variable when member fields are accessed more than once
Fix buffer leaks in Bzip2Decoder(Test)

If decompression fails, the buffer that contains the decompressed data
is not released.  Bzip2DecoderTest.testStreamCrcError() also does not
release the partial output Bzip2Decoder produces.
Checkstyle
Reduce the memory copies in JdkZlibEncoder

Motivation:

At the moment we use a lot of unnecessary memory copies in JdkZlibEncoder. This is caused by either allocate a to small ByteBuf and expand it later or using a temporary byte array.
Beside this the memory footprint of JdkZlibEncoder is pretty high because of the byte[] used for compressing.

Modification:

- Override allocateBuffer(...) and calculate the estimatedsize in there, this reduce expanding of the ByteBuf later
- Not use byte[] in the instance itself but allocate a heap ByteBuf and write directly into the byte array

Result:

Less memory copies and smaller memory footprint
Fix incorrect bytesBefore/indexOf() in ReplayingDecoderBuffer

Motivation:

bytesBefore(length, ...), bytesBefore(index, length, ...), and
indexOf(fromIndex, toIndex,...) in ReplayingDecoderBuffer are buggy.
They trigger 'REPLAY even when they don't need to.

Modification:

Implement the buggy methods properly so that REPLAYs are not triggered
unnecessarily.

Result:

Correct behvaior
[#2605] Use SO_REUSEADDR on EpollServerSocketChannel to match defaults of java.nio.ServerSocketChannel impl

Motivation:

When using openjdk and oracle jdk's nio (while using the nio transport) the ServerSocketChannel uses SO_REUSEADDR by default. Our native transport should do the same to make it easier to switch between the different implementations and get the expected result.

Modification:

Change EpollServerSocketChannelConfig to set SO_REUSEADDR on the created socket.

Result:

SO_REUSEADDR is used by default on servers.
[#2598] Add Epoll.isAvailable() which allows to check if epoll can be used.

Motivation:

At the moment there is no simple way for a user to check if the native epoll transport can be used on the running platform. Thus the user can only try to instance it and catch any exception and fallback to nio transport.

Modification:

Add Epoll.isAvailable() which allows to check if epoll can be used.

Result:

User can easily check if epoll transport can be used or not
Add missing @Test annotation
The temporary variable is no longer used in an attempt to accumulate data over onDataRead method class
Fix inconsistent code in the doc
[#2604] Not try to use sun.misc.Cleaner when on android

Motivation:

When a user tries to use netty on android it currently fails with "Could not find class 'sun.misc.Cleaner'"

Modification:

Encapsulate sun.misc.Cleaner usage in extra class to workaround this isssue.

Result:
Netty can be used on android again
Remove the deprecated methods in SPDY and HTTP

No need to keep ABI compatibility since we are working on a
backward-incompatible branch
Enable verbose:gc only when 'leak' profile is disabled

The leak profile generates a lot of garbage which makes the verbose:gc
output too large.
Upgrade JACOCO to the latest version

.. to fix the build errors triggered by the old JACOCO release
[#2615] Correctly update SelectionKey after selector rebuild

Motivation:

When a select rebuild was triggered the reference to the SelectionKey is not updated in AbstractNioChannel. This will cause a CancelledKeyException later.

Modification:

Correctly update SelectionKey reference after rebuild

Result:

Fix exception
Let EpollReuseAddrTest also work with kernel versions that not have bugfix release part
Cleanup comment / code