use netty PooledByteBufAllocator by default

Looks like by default netty uses an unpooled byte buffer allocator that creates a blocking behavior. This is the monitor usage from yourkit:

![captura de tela 2013-12-11 as 12 34 41 am](https://f.cloud.github.com/assets/831175/1719984/1f9c6b28-61f6-11e3-8b1b-7743546983bb.png)

Using the pooled version, the blocking bottleneck is solved:

![captura de tela 2013-12-11 as 12 47 28 am](https://f.cloud.github.com/assets/831175/1719998/5b0fac10-61f6-11e3-8e67-c071142eaa1a.png)