Docs: Add missing description for $pagenow global in various functions.

See #54729, #55499.

git-svn-id: https://develop.svn.wordpress.org/trunk@53060 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/user.php

@@ -510,10 +510,11 @@ function default_password_nag_edit_user( $user_ID, $old_data ) {
 /**
  * @since 2.8.0
  *
- * @global string $pagenow
+ * @global string $pagenow The filename of the current screen.
  */
 function default_password_nag() {
 	global $pagenow;
+
 	// Short-circuit it.
 	if ( 'profile.php' === $pagenow || ! get_user_option( 'default_password_nag' ) ) {
 		return;