* MXS-199: Support Causal Read in Read Write Splitting
* move most causal read logic into rwsplit router and get server type from monitor
* misc fix: remove new line
* refactor, move config to right place, replace ltrim with gwbuf_consume
* refacter a little for previous commit
* fix code style
The GWBUF shared buffer and its data is now allocated in one
chunk so that the data directly follows the shared buffer.
That way, creating a GWBUF will involve 2 and not 3 calls to
malloc and freeing one will involve 2 and not 3 calls to free.
