A+C: Matt Joiner (individual CLA)

Generated by addca.

R=gobot
CC=golang-dev
https://codereview.appspot.com/12933043
database/sql: fix accumulation of bad conns on prepared statements

Fixes an issue where prepared statements that outlive many
connections become expensive to invoke.

Fixes issue 6081

R=golang-dev
CC=bradfitz, golang-dev
https://codereview.appspot.com/12646044

Committer: Brad Fitzpatrick <bradfitz@golang.org>