Fix for ticket #2828, part II: apostrophe in site name set in installer created a...

Fix for ticket #2828, part II: apostrophe in site name set in installer created a broken config.php.

The previous commit fixed the base installer to properly quote its strings when creating config.php... but you'd actually end up with double-escaping if you had magic_quotes_gpc on. Magic quotes are evil and lame, but we gotta deal with em. :P Updated the web installer code to check for magic quotes, and to grab its variables consistently through the same interface.