Implemented '$wgWhitelistRead'.

Implemented '$wgWhitelistRead'.

$wgWhitelistRead is now defined to be an optional array
of namespace:pages a user may see unless they login.

For example:
$wgWhitelistRead = array ( ":Main_Page", "Special:Userlogin", "Wikipedia:Help" );

will restrict an anonymous user to only those pages. They are
alerted that they must login, if the try to go to another page.

If 'false', the default, the anonymous user may see all pages,
except Sysop pages, of course.