rpc: fix bug that caused private methods to attempt to be registered.
rpc: fix bug that caused private methods to attempt to be registered.

Fixes issue 1056.

R=golang-dev, adg1
CC=golang-dev
http://codereview.appspot.com/2033043

apparentlymart/golang,ssrl/go,h8liu/golang,ssrl/go,apparentlymart/golang,dsriram/golang,h8liu/golang,h8liu/golang,ssrl/go,gnanderson/go,apparentlymart/golang,ssrl/go,apparentlymart/golang,gnanderson/go,h8liu/golang,gnanderson/go,apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,tv42/old-go,h8liu/golang,apparentlymart/golang,pombredanne/go-deleteme,dsriram/golang,pombredanne/go-deleteme,dsriram/golang,tv42/old-go,pombredanne/go-deleteme,h8liu/golang,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,gnanderson/go,gnanderson/go,ssrl/go,dsriram/golang,ssrl/go,ssrl/go,tv42/old-go,gnanderson/go,pombredanne/go-deleteme,dsriram/golang,apparentlymart/golang,dsriram/golang,tv42/old-go,dsriram/golang,tv42/old-go,pombredanne/go-deleteme,h8liu/golang