Addings helper methods to HTTP/2 handler

Motivation:

Subclasses of AbstractHttp2ConnectionHandler have to implement all frame
handler methods, many of which can be ignored in many cases.  Also there
is no easy way to access the connection object.

Modifications:

Added default implementations for frame handler methods to
AbstractHttp2ConnectionHandler, and added an accessor for the
connection.

Also fixed example test for HTTP/2 with cleartext upgrade. It must have
been broken by recent commits.

Result:

AbstractHttp2ConnectionHandler is more subclass-friendly.
Introduce FastThreadLocal which uses an EnumMap and a predefined fixed set of possible thread locals

Motivation:
Provide a faster ThreadLocal implementation

Modification:
Add a "FastThreadLocal" which uses an EnumMap and a predefined fixed set of possible thread locals (all of the static instances created by netty) that is around 10-20% faster than standard ThreadLocal in my benchmarks (and can be seen having an effect in the direct PooledByteBufAllocator benchmark that uses the DEFAULT ByteBufAllocator which uses this FastThreadLocal, as opposed to normal instantiations that do not, and in the new RecyclableArrayList benchmark);

Result:
Improved performance
Introduce TextHeaders and AsciiString

Motivation:

We have quite a bit of code duplication between HTTP/1, HTTP/2, SPDY,
and STOMP codec, because they all have a notion of 'headers', which is a
multimap of string names and values.

Modifications:

- Add TextHeaders and its default implementation
- Add AsciiString to replace HttpHeaderEntity
  - Borrowed some portion from Apache Harmony's java.lang.String.
- Reimplement HttpHeaders, SpdyHeaders, and StompHeaders using
  TextHeaders
- Add AsciiHeadersEncoder to reuse the encoding a TextHeaders
  - Used a dedicated encoder for HTTP headers for better performance
    though
- Remove shortcut methods in SpdyHeaders
- Remove shortcut methods in SpdyHttpHeaders
- Replace SpdyHeaders.getStatus() with HttpResponseStatus.parseLine()

Result:

- Removed quite a bit of code duplication in the header implementations.
- Slightly better performance thanks to improved header validation and
  hash code calculation
Use FastThreadLocal in more places
export sun security packages as optional
[#2572] Correctly calculate length of output buffer before inflate to fix IndexOutOfBoundException

Motivation:

JdkZlibDecoder fails to decode because the length of the output buffer is not calculated correctly.
This can cause an IndexOutOfBoundsException or data-corruption when the PooledByteBuffAllocator is used.

Modifications:

Correctly calculate the length

Result:

No more IndexOutOfBoundsException or data-corruption.
Adding int-to-object map implementation.

Motivation:

Maps with integer keys are used in several places (HTTP/2 code, for
example). To reduce the memory footprint of these structures, we need a
specialized map class that uses ints as keys.

Modifications:

Added IntObjectHashMap, which is uses open addressing and double hashing
for collision resolution.

Result:

A new int-based map class that can be shared across Netty.
[#2573] UnpooledUnsafeDirectByteBuf.setBytes(int,ByteBuf,int,int) fails to use fast-path when src has array

Motivation:

UnpooledUnsafeDirectByteBuf.setBytes(int,ByteBuf,int,int) fails to use fast-path when src uses an array as backing storage. This is because the if else uses the wrong ByteBuf for its check.

Modifications:

- Use correct ByteBuf when check for array as backing storage
- Also eliminate unecessary check in UnpooledDirectByteBuf which always fails anyway

Result:

Faster setBytes(...) when src ByteBuf is backed by an array.

No more IndexOutOfBoundsException or data-corruption.
Fix incorrect method signature of awaitInactivity()

- Related: #2084
[#2577] ChannelOutboundBuffer.addFlush() unnecessary loop through all entries on multiple calls

Motivation:

If ChannelOutboundBuffer.addFlush() is called multiple times and flushed != unflushed it will still loop through all entries that are not flushed yet even if it is not needed anymore as these were marked uncancellable before.

Modifications:

Check if new messages were added since addFlush() was called and only if this was the case loop through all entries and try to mark the uncancellable.

Result:

Less overhead when ChannelOuboundBuffer.addFlush() is called multiple times without new messages been added.
Move calculateNewCapacity(...) to ByteBufAllocator

Motivation:

Currently we have the algorithm of calculate the new capacity of a ByteBuf implemented in AbstractByteBuf. The problem with this is that it is impossible for a user to change it if it not fits well it's use-case. We should better move it to ByteBufAllocator and so let the user implement it's own by either write his/her own ByteBufAllocator or just override the default implementation in one of our provided ByteBufAllocators.

Modifications:

Move calculateNewCapacity(...) to ByteBufAllocator and move the implementation (which was part of AbstractByteBuf) to AbstractByteBufAllocator.

Result:

The user can now override the default calculation algorithm when needed.
Make use of AtomicLongFieldUpdater.addAndGet(...) for cleaner code

Motivation:

The code in ChannelOutboundBuffer can be simplified by using AtomicLongFieldUpdater.addAndGet(...)

Modification:

Replace our manual looping with AtomicLongFieldUpdater.addAndGet(...)

Result:

Cleaner code
Small improvement in SimpleChannelInboundHandlerAdapter javadoc
Refactor FastThreadLocal to simplify TLV management

Motivation:

When Netty runs in a managed environment such as web application server,
Netty needs to provide an explicit way to remove the thread-local
variables it created to prevent class loader leaks.

FastThreadLocal uses different execution paths for storing a
thread-local variable depending on the type of the current thread.
It increases the complexity of thread-local removal.

Modifications:

- Moved FastThreadLocal and FastThreadLocalThread out of the internal
  package so that a user can use it.
- FastThreadLocal now keeps track of all thread local variables it has
  initialized, and calling FastThreadLocal.removeAll() will remove all
  thread-local variables of the caller thread.
- Added FastThreadLocal.size() for diagnostics and tests
- Introduce InternalThreadLocalMap which is a mixture of hard-wired
  thread local variable fields and extensible indexed variables
- FastThreadLocal now uses InternalThreadLocalMap to implement a
  thread-local variable.
- Added ThreadDeathWatcher.unwatch() so that PooledByteBufAllocator
  tells it to stop watching when its thread-local cache has been freed
  by FastThreadLocal.removeAll().
- Added FastThreadLocalTest to ensure that removeAll() works
- Added microbenchmark for FastThreadLocal and JDK ThreadLocal
- Upgraded to JMH 0.9

Result:

- A user can remove all thread-local variables Netty created, as long as
  he or she did not exit from the current thread. (Note that there's no
  way to remove a thread-local variable from outside of the thread.)
- FastThreadLocal exposes more useful operations such as isSet() because
  we always implement a thread local variable via InternalThreadLocalMap
  instead of falling back to JDK ThreadLocal.
- FastThreadLocalBenchmark shows that this change improves the
  performance of FastThreadLocal even more.
Merge remote-tracking branch 'origin/master'

Conflicts:
	codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketServerProtocolHandshakeHandler.java