[FIX] version: Only display updates available message if prefs.feature_version_checks or forcecheck is set, as well as prefs.tiki_needs_upgrade.
Prevents spurious upgrade notices showing when feature_version_checks is off.
Not a backport from 11.x as it's done differently there now.

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/9.x@47383 b456876b-0849-0410-b77d-98878d47e9d5