Handler Unit Test Bug

Motivation:
There is a bug in the JettySslEngineTest where the interface receiving a message does not do a latch.countDown().
This causes each test to be subject to the CountDownLatch timeout period instead of being notified right when an event occurs.

Modifications:
- The JettySslEngineTest message handler will call the appropriate latch.countDown after a message is received

Result:
JettySslEngineTest will not be subject to waiting the timeout period even if the message is correctly received
[#2867] Workaround performance issue with IPv4-mapped-on-IPv6 addresses

Motivation:

InetAddress.getByName(...) uses exceptions for control flow when try to parse IPv4-mapped-on-IPv6 addresses. This is quite expensive.

Modifications:

Detect IPv4-mapped-on-IPv6 addresses in the JNI level and convert to IPv4 addresses before pass to InetAddress.getByName(...) (via InetSocketAddress constructor).

Result:

Eliminate performance problem causes by exception creation when parsing IPv4-mapped-on-IPv6 addresses.
Allow to write CompositeByteBuf directly via EpollDatagramChannel. Related to [#2719]

Motivation:

On linux it is possible to use the sendMsg(...) system call to write multiple buffers with one system call when using datagram/udp.

Modifications:

- Implement the needed changes and make use of sendMsg(...) if possible for max performance
- Add tests that test sending datagram packets with all kind of different ByteBuf implementations.

Result:

Performance improvement when using CompoisteByteBuf and EpollDatagramChannel.
Add support for sendmmsg(...) and so allow to write multiple DatagramPackets with one syscall. Related to [#2719]

Motivation:

On linux with glibc >= 2.14 it is possible to send multiple DatagramPackets with one syscall. This can be a huge performance win and so we should support it in our native transport.

Modification:

- Add support for sendmmsg by reuse IovArray
- Factor out ThreadLocal support of IovArray to IovArrayThreadLocal for better separation as we use IovArray also without ThreadLocal in NativeDatagramPacketArray now
- Introduce NativeDatagramPacketArray which is used for sendmmsg(...)
- Implement sendmmsg(...) via jni
- Expand DatagramUnicastTest to test also sendmmsg(...)

Result:

Netty now automatically use sendmmsg(...) if it is supported and we have more then 1 DatagramPacket in the ChannelOutboundBuffer and flush() is called.
Fix buffer leak in DatagramUnicastTest caused by incorrect usage of CompositeByteBuf

Motivation:

Due incorrect usage of CompositeByteBuf a buffer leak was introduced.

Modifications:

Correctly handle tests with CompositeByteBuf.

Result:

No more buffer leaks
Directly write CompositeByteBuf if possible without memory copy. Related to [#2719]

Motivation:

In linux it is possible to write more then one buffer withone syscall when sending datagram messages.

Modifications:

Not copy CompositeByteBuf if it only contains direct buffers.

Result:

More performance due less overhead for copy.
HTTP Content Decoder Cleanup Bug

Motiviation:
The HTTP content decoder's cleanup method is not cleaning up the decoder correctly.
The cleanup method is currently doing a readOutbound on the EmbeddedChannel but
for decoding the call should be readInbound.

Modifications:
-Change readOutbound to readInbound in the cleanup method

Result:
The cleanup method should be correctly releaseing unused resources
Correct javadoc typo in IdleStateHandler example code
HTTP/2 Cipher Suite Support

Motivation:
The HTTP/2 specification places restrictions on the cipher suites that can be used. There is no central place to pull the ciphers that are allowed by the specification, supported by different java versions, and recommended by the community.

Modifications:
-HTTP/2 will have a security utility class to define supported ciphers
-netty-handler will be modified to support filtering the supplied list of ciphers to the supported ciphers for the current SSLEngine

Result:
-Netty provides unified support for HTTP/2 cipher lists and ciphers can be pruned by currently supported ciphers
Add missing calls to childGroup().shutdownGraceFully()

Motivation:

The ServerBootrap's child group would not be shutdown.

Modification:

Add missing shutdownGracefully() call.

Result:

The child group is shutdown correctly.
Shutdown Executor on MultithreadEventLoopGroup shutdown. Fixes #2837

Motivation:

Currently the Executor created by (Nio|Epoll)EventLoopGroup is not correctly shutdown.
This might lead to resource shortages, due to resources not being freed asap.

Modifications:

If (Nio|Epoll)EventLoopGroup create their internal Executor via a constructor
provided `ExecutorServiceFactory` object or via
MultithreadEventLoopGroup.newDefaultExecutorService(...) the ExecutorService.shutdown()
method will be called after (Nio|Epoll)EventLoopGroup is shutdown.

ExecutorService.shutdown() will not be called if the Executor object was passed
to the (Nio|Epoll)EventLoopGroup (that is, it was instantiated outside of Netty).

Result:

Correctly release resources on (Nio|Epoll)EventLoopGroup shutdown.
Correcting HttpDecoder SuppressWarnings parameter

Motiviation:
The HttpContentDecoder.getTargetContentEncoding has a SuppressWarnings(unused) on its parameter.
This should be SuppressWarnings(UnusedParameters).

Modifications:
SuppressWarnings(unused) -> SuppressWarnings(UnusedParameters)

Result:
Correctly suppressing warnings due to HttpContentDecoder.getTargetContentEncoding
HTTP/2 Data Decompression

Motivation:
The HTTP/2 codec does not provide a way to decompress data. This functionality is supported by the HTTP codec and is expected to be a commonly used feature.

Modifications:
-The Http2FrameReader will be modified to allow hooks for decompression
-New classes which detect the decompression from HTTP/2 header frames and uses that decompression when HTTP/2 data frames come in
-New unit tests

Result:
The HTTP/2 codec will provide a means to support data decompression