added datatype/hello extensions constants

Change-Id: I6fc0d518c4875ce53c639439ab130400290820b3
Reviewed-on: http://review.couchbase.org/37553
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
propagate datatype field to #upr_mutation{}

Change-Id: I7ffefaa3f7e3008ebefaf5e3756ae50fdc4918f8
Reviewed-on: http://review.couchbase.org/37554
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>