Fix AdaptiveRecvByteBufAllocator.getSizeTableIndex()
SPDY: handle too large header blocks

- Forward-ported 22b8a96e044b77e5fadc5a1217080a1f9c69aa9c
[maven-release-plugin] prepare release netty-4.0.0.CR6
[maven-release-plugin] prepare for next development iteration
Improve the utilization of subpage pools

.. by avoiding the overly frequent removal of a subpage from a pool

This change makes sure that the unused subpage is not removed when there's no subpage left in the pool.  If the last subpage is removed from the pool, it is very likely that the allocator will create a new subpage very soon again, so it's better not remove it.
Fix regression introduced by 0364265f4692b2f2f28ab36037c4ab6f3c242eae which could lead to corrupt attribute values
[#1454] Fix IndexOutOfBoundsException which was thrown if last component of a CompositeByteBuf was removed