[#2280] Correct logic in Native.finishConnect. Fix use of optval parameter in c getOption function. In epoll event loop, check that channel is open before processing event.
Fix buffer leak in test which was introduced while implement ZLIB_OR_NONE support. Related to [#2269]
added support for empty query parameters
[#2297] Correctly close all registered Channels on EpollEventLoop.closeAll()
ipfilter implementation for netty 4/5 [#2129]
Use bitwise operations to choose next EventExecutor if number of EventExecutors is power of two
Move the pull request guide to the developer guide

Motivation:

CONTRIBUTING.md is useful only because it lets Github show a user the
link to it so the user can check what information we need before
submitting a bug report.  However, Github does not do the same for a
pull request submission form, and thus there's no reason to keep the
information about how to submit a good pull request in CONTRIBUTING.md.

Modification:

Replace the section about issuing a pull request with the link to the
official developer guide.

Result:

CONTRIBUTING.md is easier to maintain.
Overall clean-up of ipfilter package

Motivation:

Recently merged ipfilter package has the following problems:
* AbstractIpFilterHandler could be improved to support any SocketAddress types rather than only InetSocketAddress.
* AbstractIpFilterHandler can be removed immediately after decision is made rather than keeping the outcome of the decision as an attribute.
* AbstractIpFilterHandler doesn't have a hook for the accepted addresses.
* The hook method (reject()) needs to be named in line with other handler methods (i.e. channelRejected())
* IpFilterRuleHandler should allow accepting zero rules - it's particularly useful for machine-configured setup (i.e. specifying zero rules disables ipfilter).
* IpFilterRuleType.ALLOW/DENY should be ACCEPT/REJECT for consistency.

Modifications:

* AbstractIpFilterHandler has been renamed to AbstractRemoteAddressFilter and now uses type parameter.
* Added channelAccepted() and renamed reject() to channelRejected()
* Added ChannelHandlerContext as a parameter of accept() so that accept() can add a listener to the closeFuture() of the channel. This way, UniqueIpFilter continue working even if we remove the filtering handler early.
* Various renames
  * IpFilterRuleHandler -> RuleBasedIpFilter
  * UniqueIpFilterHandler -> UniqueIpFilter

Result:

* Much cleaner API with more extensibility
Do not use finally to propagate events in AbstractRemoteAddressFilter

Motivation:

We don't really need to propagate an event when handling the event fails.

Modifications:

Do not use finally block in AbstractRemoteAddressFilter

Result:

AbstractRemoteaddressFilter does not forward an event in case of failure.
Add capacity limit to Recycler / Optimize when assertion is off

Motivation:

- As reported recently [1], Recycler's thread-local object pool has unbounded capacity which is a potential problem.
- It accesses a hash table on each push and pop for debugging purposes.  We don't really need it besides debugging Netty itself.

Modifications:

- Introduced the maxCapacity constructor parameter to Recycler.  The default default maxCapacity is retrieved from the system property whose default is 256K, which should be plenty for most cases.
- Recycler.Stack.map is now created and accessed only when assertion is enabled for Recycler.

Result:

- Recycler does not grow infinitely anymore.
- If assertion is disabled, Recycler should be much faster.

[1] https://github.com/netty/netty/issues/1841
Remove condition in ChannelHandlerAdapter.isSharable() by caching the result of the annotation lookup.

Motivation:
Remove the synchronization bottleneck and so speed up things

Modifications:
Introduce a ThreadLocal cache that holds mappings between classes of ChannelHandlerAdapater implementations and the result of checking if the @Sharable annotation is present.
This way we only will need to do the real check one time and server the other calls via the cache. A ThreadLocal and WeakHashMap combo is used to implement the cache
as this way we can minimize the conditions while still be sure we not leak class instances in containers.

Result:
Less conditions during adding ChannelHandlerAdapter to the ChannelPipeline
Fix checkstyle errors introduced by f0d1bbd63ec910b9c5bccc925bdf0b0f55db1f9c
[#2308] Use SelectorProvider.open*() to open NIO channels and so remove condition when create new NIO channels.

Motivation:
At the moment we use SocketChannel.open(), ServerSocketChannel.open() and DatagramSocketChannel.open(...) within the constructor of our
NIO channels. This introduces a bottleneck if you create a lot of connections as these calls delegate to SelectorProvider.provider() which
uses synchronized internal. This change removed the bottleneck.

Modifications:
Obtain a static instance of the SelectorProvider and use SelectorProvider.openSocketChannel(), SelectorProvider.openServerSocketChannel() and
SelectorProvider.openDatagramChannel(). This eliminates the bottleneck as SelectorProvider.provider() is not called on every channel creation.

Result:
Less conditions when create new channels.
Remove sniffer whitelist entries for NIO.2

Motivation:
Cleanup pom.xml file.

Modifications:
Remove sniffer whitelist entries for NIO.2 as we not include a NIO.2 bases transport anymore.

Result:
Less entries in pom.xml
[#2307] Remove synchronized bottleneck in SingleThreadEventExecutor.execute(...)

Motivation:
Remove the synchronization bottleneck in startThread() which is called by each execute(..) call from outside the EventLoop.

Modifications:
Replace the synchronized block with the use of AtomicInteger and compareAndSet loops.

Result:
Less conditions during SingleThreadEventExecutor.execute(...)
Fix limit computation of NIO ByteBuffers obtained via ReadOnlyByteBufferBuf.nioBuffer

Motivation:

When starting with a read-only NIO buffer, wrapping it in a ByteBuf,
and then later retrieving a re-wrapped NIO buffer the limit was getting
too short.

Modifications:

Changed ReadOnlyByteBufferBuf.nioBuffer(int,int) to compute the
limit in the same manner as the internalNioBuffer method.

Result:

Round-trip conversion from NIO to ByteBuf to NIO will work reliably.
[#2305] Fix issue related to decoding post request raized an exception due to a split of information by chunk not correctly taken into account by the decoder

Motivation:

If the last item analyzed in a previous received HttpChunk/HttpContent was a part of an attribute's name, the read index was not set to the new right place and therefore raizing an exception in some case (since the "new" name analyzed is empty, which is not allowed so the exception).

What appears there is that the read index should be reset to the last valid position encountered whatever the case. Currently it was set when only when there is an attribute not already finished (name is ok, but content is possibly not).

Therefore the issue is that elements could be rescanned multiple times (including completed elements) and moreover some bad decoding can occur such as when in a middle of an attribute's name.

Modifications:

To fix this issue, since "firstpos" contains the last "valid" read index of the decoding (when finding a '&', '=', 'CR/LF'), we should add the setting of the read index for the following cases:

'lastchunk' encountered, therefore finishing the current buffer
any other cases than current attribute is not finished (name not found yet in particular)
So adding for this 2 cases:

undecodedChunk.readerIndex(firstpos);

Result:

Now the decoding is done once, content is added from chunk/content to chunk/content, name is decoded correctly even if in the middle of 2 chunks/contents.
A Junit test code was added: testChunkCorrect that should not raized any exception.
[#2262] Fix NPE triggered by unresolveable InetSocketAddress in epoll transport

Motivation:
At the moment when an unresolvable InetSocketAddress is passed into the epoll transport a NPE is thrown

Modifications:
Add check in place which will throw an UnknownHostException if an InetSocketAddress could not been resolved.

Result:
Proper handling of unresolvable InetSocketAddresses
[#2323] Make it clear a Channel must be closed to release all resources

Motivation:
Ensure the user know the Channel must be closed to release resources like filehandles.

Modifications:
Add some extra javadoc.

Result:
More clear documentation
[#2326] Add constructor to NioServerSocketChannel which accepts a ServerSocketChannel

Motivation:
Allow the user to create a NioServerSocketChannel from an existing ServerSocketChannel.

Modifications:
Add an extra constructor

Result:
Now the user is be able to create a NioServerSocketChannel from an existing ServerSocketChannel, like he can do with all the other Nio*Channel implemntations.