language_attributes() undefined in 5 minute install

[alanjcastonguay]

In a freshly emerged copy of wp2.1, there's no wp-config.php file. Traditionally, when a user visits the blog in this state, the 5 minute installer takes over, linking the user to /wordpress/wp-admin/setup-config.php.

• As of [4307], this uses wp_die()
  
• As of [4259], wp_die() uses language_attributes() in the <html> tag
  
• language_attributes() is in source:/trunk/wp-includes/general-template.php@4376#L876​
  
• general-template.php is require_once()'d by source:/trunk/wp-settings.php@4376#L147​
  
• wp-settings.php is require_once()'d by wp-config.php

If wp-config.php does not exist, wp_die() cannot output language_attributes, and throws a PHP Fatal error instead of displaying the useful error message. Depending on PHP config, the user is left with a blank screen, or the error:

PHP Fatal error: Call to undefined function language_attributes() in /Users/alan/Sites/wp21/wp-includes/functions.php on line 1112

I suggest that wp_die() failures to this degree don't bother outputting language information, and just continue on to dumping the error message and die().

[alanjcastonguay]

diff to add function_exists test

[markjaquith]

(In [4379]) wp_die() fix for 5 minute install from alanjcastonguay. fixes #3231