wp_check_php_mysql_versions() during setup and install. see #17934.

git-svn-id: https://develop.svn.wordpress.org/trunk@18374 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/load.php

@@ -2,6 +2,8 @@
 /**
  * These functions are needed to load WordPress.
  *
+ * This file must be parsable by PHP4.
+ *
  * @package WordPress
  */
 
@@ -95,6 +97,9 @@ function wp_fix_server_vars() {
  *
  * Dies if requirements are not met.
  *
+ * This function must be able to work without a complete environment set up. In wp-load.php, for
+ * example, WP_CONTENT_DIR is defined and version.php is included before this function is called.
+ *
  * @access private
  * @since 3.0.0
  */