SwappedByteBuf.unwrap() should return null

Fixes #945.  For swapped wrapped buffers, it should not return null.
Ensure cascaded derivation of a buffer does not result in an infinitely nested buffer.
Hide the constructors of ChannelOption to force using dedicated option type
[#910] Make use of ByteBufHolder in SPDY, HTTP multipart and WebSockets to allow for buffer pooling
Tighten visibility
Remove 'get' prefix
Remove 'get' prefix
Fix checkstyle
Prevent possible ClassCastException
[#907] Prevent IllegalBufferAccessException which could be triggered if inboundBufferUpdated(), flush(..), write(..) was triggered after the channel was closed
[#907] Prevent IllegalBufferAccessException which could be triggered if inboundBufferUpdated() was called once the channel was closed
Tiny optimization
Remove io.netty.monitor as discussed in #922
Enable resource leak detection during test
Consistent exception messages
Fix failing tests
Fix leaks in buffer tests
Fix APIviz panic
[#907] Stop flush if one outboundbuffer was freed and do the same for inboundBufferUpdated if an inboundbuffer was freed
[#952] Allow to switch to single message decoding mode on the fly