Fix chunk type for stream identifier

Motivation:
The problem with the current snappy implementation is that it does
not comply with framing format definition found on
https://code.google.com/p/snappy/source/browse/trunk/framing_format.txt

The document describes that chunk type of the stream identifier is defined
as 0xff. The current implentation uses 0x80.

Modifications:
This patch replaces the first byte of the chunk type of the stream identifier
with 0xff.

Result:
After this modification the snappy implementation is compliant to the
framing format described at
https://code.google.com/p/snappy/source/browse/trunk/framing_format.txt.
This results in a better compatibility with other implementations.
Feed only a single SSL record to SSLEngine.unwrap()

Motivation:

Some SSLEngine implementations violate the contract and raises an
exception when SslHandler feeds an input buffer that contains multiple
SSL records to SSLEngine.unwrap(), while the expected behavior is to
decode the first record and return.

Modification:

- Modify SslHandler.decode() to keep the lengths of each record and feed
  SSLEngine.unwrap() record by record to work around the forementioned
  issue.
- Rename unwrap() to unwrapMultiple() and unwrapNonApp()
- Rename unwrap0() to unwrapSingle()

Result:

SslHandler now works OpenSSLEngine from finagle-native.  Performance
impact remains unnoticeable.  Slightly better readability. Fixes #2116.
Stop ThreadLocalRandom's initial seed generation immediately on interruption

Motivation:

ThreadLocalRandomTest reveals that ThreadLocalRandom's initial seed generation loop becomes tight if the thread is interrupted.
We currently interrupt ourselves inside the wait loop, which will raise an InterruptedException again in the next iteration, resulting in infinite (up to 3 seconds) exception construction and thread interruptions.

Modification:

- When the initial seed generator thread is interrupted, break out of the wait loop immediately.
- Log properly when the initial seed generation failed due to interruption.
- When failed to generate the initial seed, interrupt the generator thread just in case the SecureRandom implementation handles it properly.
- Make the initial seed generator thread daemon and handle potential exceptions raised due to the interruption.

Result:

No more tight loop on interruption.  More robust generator thread termination. Fixes #2412
Use correct generics for TCP_KEEPIDLE, TCP_KEEPINTVL and TCP_KEEPCNT in EpollChannelOption. Part of [#2396]

Motivation:
Currently the generics used for TCP_KEEPIDLE, TCP_KEEPINTVL and TCP_KEEPCNT are incorrect.

Modifications:
Use Integer as type

Result:
User can use TCP_KEEPIDLE, TCP_KEEPINTVL and TCP_KEEPCNT as expected
[#2400] Not close LocalChannel during deregister() to allow register to other EventLoop

Motivation:
At the moment it is not possible to deregister a LocalChannel from its EventLoop and register it to another one as the LocalChannel is closed during the deregister.

Modification:
Not close the LocalChannel during dergister

Result:
It is now possible to deregister a LocalChannel and register it to another EventLoop
[#2414] Fix RuntimeException during modify events via EpollEventLoop

Motivation:
We are currently try to modify the events via EpollEventLoop even when the channel was closed before and so the fd was set to -1. This fails with a RuntimeException in this case.

Modification:
Always check if the Channel is still open before try to modify the events.

Result:
No more RuntimeException because of a not open channel
[#2414] Fix IllegalStateException when try to configure AbstractEpollChannel once it is deregistered

Motivation:
AbstractEpollChannel.clearEpollIn() throws an IllegalStateException if a user tries to change the autoRead configuration for the Channel and the Channel is not registered on an EventLoop yet. This makes it for example impossible to set AUTO_READ to false via the ServerBootstrap as the configuration is modifed before the Channel is registered.

Modification:
Check if the Channel is registered and if not just modify the flags directly so they are respected once the Channel is registered

Result:
It is possible now to configure AUTO_READ via the ServerBootstrap
Merge upstream 4.0 branch into proxy_protocol