(Issue #661) Allow People with Siteadmin Priv to PM Uncomfirmed Accounts

Allows somebody to PM an unvalidated account (unconfirmed email address)
if they have the siteadmin:* priv. Fixes #661.
Merge pull request #704 from hotlevel4/bug661/PMUnverifiedAccounts

(Issue #661) Allow People with Siteadmin Priv to PM Uncomfirmed Accounts