Allow load if HTTP authentication is required

I noticed how the user is redirected to an error message if the site is
not launched from localhost. Perhaps we should provide a way to allow
this site to be used on a remote server provided that it is in a
directory requiring HTTP authentication?

According to PHP's page on HTTP authentication
<http://php.net/manual/en/features.http-auth.php>,
$_SERVER['REMOTE_USER'] should be set if external authentication (from a
.htaccess file or what have you) was needed to reach the page and
$_SERVER['PHP_AUTH_USER'] should be set if PHP's HTTP authentication
methods were used.

Let me know what you think...
Updated HTTP auth check

Well... somehow I never read that second sentence of the [empty()
spec](http://us1.php.net/empty) description that says it doesn't produce
any warnings if the variable you pass doesn't exist, so yes, isset()
would be redundant, for sure. And yes, an initially empty false value is
a little easier.

So, it assumes there's no such authorization unless
`$_SERVER['REMOTE_USER']` isn't empty or it can find the "Authorization"
Apache request header. If HTTP authorization is being achieved by way of
passing values to `header()`, `$_SERVER['REMOTE_USER']` would need to be
set in the authentication process (such as with the value of
`$_SERVER['PHP_AUTH_USER']`) if they would like to use this utility.
What are your thoughts?