added HTML5 specified regexp for valid email addresses
added HTML5 specified regexp for valid email addresses

See
http://www.w3.org/TR/html5/states-of-the-type-attribute.html#e-mail-state

That's same regexp that html5 implementations are required to use for
type=email inputs validation.

Note: HTML5 explicitly and willfully violates some RFCs, but that
still seems reasonable.

Change-Id: I223ff61d007504ed5e7cb7f8f0c2f7153d8fcc51
Reviewed-on: http://review.couchbase.org/11761
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Reviewed-by: Steve Yen <ef850f73f7832052d3c6d9b5ddd3a1716d9a57f1@gmail.com>

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