mime: add a TODO, fix the format of an error
mime: add a TODO, fix the format of an error

R=r, rsc1
CC=golang-dev
http://codereview.appspot.com/4440054

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