C: add googler Matt Brown mdbrown@google.com

R=golang-dev, rsc
CC=golang-dev
https://codereview.appspot.com/7444045
strconv: use Quote to escape the input string for failed conversion errors

This reveals the presence of control and non-printable characters in the
errors returned by the Parse functions.  Also add unit tests for NumError.

R=golang-dev, r, rsc
CC=golang-dev
https://codereview.appspot.com/7393075

Committer: Rob Pike <r@golang.org>