Shorter names for unexported functions in reducers module

Change-Id: I721084eddd5c7852537e240f53148e0338d8a85b
Reviewed-on: http://review.couchbase.org/27362
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>