The existing implementation doesn't handle
comment constructions in email address.
So addresses that are consistent with RFC 5322
don't parse at all.

Fixes #21257

Change-Id: Iae3ba951dfb26b7cf0e1885a680bbceb9123d6d5
Reviewed-on: https://go-review.googlesource.com/53550
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>