Docs: Improve various globals documentation, as per documentation standards.

Props upadalavipul.
See #57069, #56792.

Built from https://develop.svn.wordpress.org/trunk@54953


git-svn-id: http://core.svn.wordpress.org/trunk@54505 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/ms-deprecated.php

@@ -179,6 +179,8 @@ function validate_email( $email, $check_domain = true) {
  * @deprecated 3.0.0 Use wp_get_sites()
  * @see wp_get_sites()
  *
+ * @global wpdb $wpdb WordPress database abstraction object.
+ *
  * @param int    $start      Optional. Offset for retrieving the blog list. Default 0.
  * @param int    $num        Optional. Number of blogs to list. Default 10.
  * @param string $deprecated Unused.