Bit tricks to check for and calculate power of two.

Motivation:
I was studying the code and thought this was simpler and easier to
understand.

Modifications:
Replaced the for loop and if conditions, with a simple implementation.

Result:
Code is easier to understand.
Replace usage of System.currentTimeMillis() with System.nanoTime()

Motivation:

Currently we use System.currentTimeMillis() in our timeout handlers this is bad
for various reasons like when the clock adjusts etc.

Modifications:

Replace System.currentTimeMillis() with System.nanoTime()

Result:

More robust timeout handling
Fix and simplify freeing a direct buffer / Fix Android support

Motivation:

6e8ba291cfcb325fe4397a8e7db43579070e7a07 introduced a regression in Android because Android does not have sun.nio.ch.DirectBuffer (see #2330.)  I also found PlatformDependent0.freeDirectBuffer() and freeDirectBufferUnsafe() are pretty much same after the commit and the unsafe version should be removed.

Modifications:

- Do not use the pooled allocator in Android because it's too resource hungry for Androids.
- Merge PlatformDependent0.freeDirectBuffer() and freeDirectBufferUnsafe() into one method.
- Make the Unsafe unavailable when sun.nio.ch.DirectBuffer is unavailable.  We could keep the Unsafe available and handle the sun.nio.ch.DirectBuffer case separately, but I don't want to complicate our code just because of that.  All supported JDK versions have sun.nio.ch.DirectBuffer if the Unsafe is available.

Result:

Simpler code. Fixes Android support (#2330)
Fixing javadoc ascii table for ChannelFuture

Motivation:
The current ascii table [1] showing the various states that a ChannelFuture
can be in, but the table is slightly "off" for the 'cause'.

Modifications:
- Updated the ascii table to display nicely.

Result:
Easier to read the states of a ChannelFuture.

[1] http://netty.io/5.0/api/io/netty/channel/ChannelFuture.html
Implement Thread caches for pooled buffers to minimize conditions. This fixes [#2264] and [#808].

Motivation:
Remove the synchronization bottleneck in PoolArena and so speed up things

Modifications:

This implementation uses kind of the same technics as outlined in the jemalloc paper and jemalloc
blogpost https://www.facebook.com/notes/facebook-engineering/scalable-memory-allocation-using-jemalloc/480222803919.

At the moment we only cache for "known" Threads (that powers EventExecutors) and not for others to keep the overhead
minimal when need to free up unused buffers in the cache and free up cached buffers once the Thread completes. Here
we use multi-level caches for tiny, small and normal allocations. Huge allocations are not cached at all to keep the
memory usage at a sane level. All the different cache configurations can be adjusted via system properties or the constructor
directly where it makes sense.

Result:
Less conditions as most allocations can be served by the cache itself
Reduce the time taken by NetUtil and DefaultChannelId class initialization

Motivation:

As reported in #2331, some query operations in NetworkInterface takes much longer time than we expected.  For example, specifying -Djava.net.preferIPv4Stack=true option in Window increases the execution time by more than 4 times.  Some Windows systems have more than 20 network interfaces, and this problem gets bigger as the number of unused (virtual) NICs increases.

Modification:

Use NetworkInterface.getInetAddresses() wherever possible.
Before iterating over all NICs reported by NetworkInterface, filter the NICs without proper InetAddresses.  This reduces the number of candidates quite a lot.
NetUtil does not query hardware address of NIC in the first place but uses InetAddress.isLoopbackAddress().
Do not call unnecessary query operations on NetworkInterface.  Just get hardware address and compare.

Result:

Significantly reduced class initialization time, which should fix #2331.
Prefer the NIC with global IP address when getting the default machine ID

Motivation:

When there are two MAC addresses which are good enough, we can choose the one with better IP address rather than just choosing the first appeared one.

Modification:

Replace isBetterAddress() with compareAddresses() to make it return if both addresses are in the same preference level.
Add compareAddresses() which compare InetAddresses and use it when compareAddress(byte[], byte[]) returns 0 (same preference)

Result:

More correct primary MAC address detection
Use the length of MAC address as the last property to compare to get the best MAC address

Motivation:

Some operating systems like Windows 7 uses a valid globally unique EUI-64 MAC address for a virtual device (e.g. 00:00:00:00:00:00:00:E0), and because it's usually longer than the legit MAC-48 address, we should not use the length of MAC address when two MAC addresses are of the same quality.  Instead, we should compare the INET address of the NICs before comparing the length of the MAC addresses.

Modification:

Compare the length of MAC addresses as a last resort.

Result:

Correct MAC address detection in Windows with IPv6 enabled.
Use SecureRandom.generateSeed() to generate ThreadLocalRandom's initialSeedUniquifier

Motivation:

Previously, we used SecureRandom.nextLong() to generate the initialSeedUniquifier.  This required more entrophy than necessary because it has to 1) generate the seed of SecureRandom first and then 2) generate a random long integer.  Instead, we can use generateSeed() to skip the step (2)

Modifications:

Use generateSeed() instead of nextLong()

Result:

ThreadLocalRandom requires less amount of entrphy to start up
Adding support for specifying preflight response headers.

Motivation:

An intermediary like a load balancer might require that a Cross Origin
Resource Sharing (CORS) preflight request have certain headers set.
As a concrete example the Elastic Load Balancer (ELB) requires the
'Date' and 'Content-Length' header to be set or it will fail with a 502
error code.

This works is an enhancement of https://github.com/netty/netty/pull/2290

Modifications:

CorsConfig has been extended to make additional HTTP response headers
configurable for preflight responses. Since some headers, like the
'Date' header need to be generated each time, m0wfo suggested using a
Callable.

Result:

By default, the 'Date' and 'Content-Lenght' headers will be sent in a
preflight response. This can be overriden and users can specify
any headers that might be required by different intermediaries.
Fixing CorsConfigTest failure under Java 8.

Motivation:
When running the build with Java 8 the following error occurred:

java: reference to preflightResponseHeader is ambiguous
  both method
  <T>preflightResponseHeader(java.lang.CharSequence,java.lang.Iterable<T>)
  in io.netty.handler.codec.http.cors.CorsConfig.Builder and method
  <T>preflightResponseHeader(java.lang.String,java.util.concurrent.Callable<T>)
  in io.netty.handler.codec.http.cors.CorsConfig.Builder match

The offending class was CorsConfigTest and its shouldThrowIfValueIsNull
which contained the following line:
withOrigin("*").preflightResponseHeader("HeaderName", null).build();

Modifications:
Updated the offending method with to supply a type, and object array, to
avoid the error.

Result:
After this I was able to build with Java 7 and Java 8
[#2234] Use QueryStringDecoder.decodeComponent to decode url-encoded data instead of Java's URLDecoder.

Motivation:
Previously, we used URLDecoder.decode(...) to decode url-encoded data. This generates a lot of garbage and takes a considerable amount of time.

Modifications:
Replace URLDecoder.decode(...) with QueryStringDecoder.decodeComponent(...)

Result:
Less garbage to GC and faster decode processing.
Make sure the local / remote InetSocketAddres can be obtained. Part of [#2262]

Motivation:
Make sure the remote/local InetSocketAddress can be obtained correctly

Modifications:
Set the remote/local InetSocketAddress after a bind/connect operation was performed

Result:
It is possible to still access the informations even after the fd became invalid. This mirror the behaviour of NIO.
Allow specifying `SelectorProvider` when constructing an NIO channel #2311

Motivation:

At the moment we use the system-wide default selector provider for this invocation of the Java virtual machine when constructing a new NIO channel, which makes using an alternative SelectorProvider practically useless.
This change allows user specify his/her preferred SelectorProvider.

Modifications:

Add SelectorProvider as a param for current `private static *Channel newSocket` method of NioSocketChannel, NioServerSocketChannel and NioDatagramChannel.
Change default constructors of NioSocketChannel, NioServerSocketChannel and NioDatagramChannel to use DEFAULT_SELECTOR_PROVIDER when calling newSocket(SelectorProvider).
Add new constructors for NioSocketChannel, NioServerSocketChannel and NioDatagramChannel which allow user specify his/her preferred SelectorProvider.

Result:

Now users can specify his/her preferred SelectorProvider when constructing an NIO channel.
Fixing spelling/typo in javadocs for EventExecutor.

Motivation:
Minor spelling/typo correction for EventExecutor's newSucceededFuture and
newFailedFuture javadocs.

Modifications:
Just correcting the spelling/typo.

Result:
Improve the javadocs.
Remove overridden next() method in EventLoop interface.

Motivation:
EventLoop overrides the next() method with the same signature of its
super class EventLoopGroup.

Modifications:
Remove the duplicate method declaration from the EventLoop interface.

Result:
Perhaps makes the API slightly more readable as there is one less
method.
[#2339] Reduce memory usage in ProtobufVarint32LengthFieldPrepender

Motivation:

Reduce memory usage in ProtobufVarint32LengthFieldPrepender.

Modifications:

Explicit set the buffer size that is needed for the header (between 1 and 5 bytes).

Result:

Less memory usage in ProtobufVarint32LengthFieldPrepender.
Deleting redundant needsFlush boolean

Motivation:

In ChunkedWriteHandler, there is a redundant variable that servers
no purpose. It implies that under some conditions you might not want
to flush.

Modifications:

Removed the variable and the if condition that read it. The boolean
was always true so just removing the if statement was fine.

Result:

Slightly less misleading code.
Adding origins whitelist support for CORS

Motivation:
Currently the CORS support only handles a single origin, or a wildcard
origin. This task should enhance Netty's CORS support to allow multiple
origins to be specified. Just being allowed to specify one origin is
particulary limiting when a site support both http and https for
example.

Modifications:
- Updated CorsConfig and its Builder to accept multiple origins.

Result:
Users are now able to configure multiple origins for CORS.

[https://github.com/netty/netty/issues/2346]
[#2349] Correctly handle cancelled ChannelPromise in DefaultChannelHandlerContext

Motivation:
At the moment an IllegalArgumentException will be thrown if a ChannelPromise is cancelled while propagate through the ChannelPipeline. This is not correct, we should just stop to propagate it as it is valid to cancel at any time.

Modifications:
Stop propagate the operation through the ChannelPipeline once a ChannelPromise is cancelled.

Result:
No more IllegalArgumentException when cancel a ChannelPromise while moving through the ChannelPipeline.