spec: skip carriage returns in raw literals
spec: skip carriage returns in raw literals

This change guarantees that whether the line ending convention
when the source is created includes carriage returns is irrelevant
to the value of the string. See issue 680.

The compilers do not yet implement this.

R=golang-dev, adg, r, gri, rsc, iant
CC=golang-dev
http://codereview.appspot.com/5491043
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go