database/sql: use method values instead of generating closures
database/sql: use method values instead of generating closures

Reduces garbage.

R=adg, r
CC=dsymonds, gobot, golang-dev
https://codereview.appspot.com/9088045

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