Strip whitespace from STMP server names.

The STMP server configuration would fail if there was trailing whitespace on the
server name. This was a problem when copy/pasting text into the form.

Testing done:
Produced the bug with an smtp server "smtp.gmail.com     " and triggered an
email event (registration for new user). Log produced an error: "Unknown host".
Added the changes on the diff and tried again, the email is sent and the value
that is saved is stripped of the redudant spaces.

Reviewed at http://reviews.reviewboard.org/r/3759/
Fixes bug 2620.