hrpc: Simplify definition of comparators.
hrpc: Simplify definition of comparators.

Since we ultimately just wrap the protobuf types, let's use typedefs to
avoid having to duplicate all the definitions and copy the data back and
forth between our structs and the pb structs.

Change-Id: I0a09440cd3b3ee3c51fdf65ae11d84f19d61ef31

tsuna/gohbase,tempbottle/gohbase,henrylee2cn/gohbase,dougklein/gohbase,dougklein/gohbase