CRM-15248 - footer.tpl - For front-end users, redact point-release.

On one hand, giving a precise version can help attackers match their targets
with exploits.  On the other hand, giving some kind of version indication is
useful for support and marketing.  This PR attempts to balance the interests
by giving a precise version ("Powered by CiviCRM 4.4.6") to users with
permission "access CiviCRM" while giving a coarse-version ("Powered by
CiviCRM 4.4") to anyone else.