Add missing doc blocks for pluggable.php.

Correct some `@return` values.
`is_user_logged_in()` can simply return the `->exists()` call instead of if/else'ing true/false.

See #32444.

Built from https://develop.svn.wordpress.org/trunk@32614


git-svn-id: http://core.svn.wordpress.org/trunk@32584 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.3-alpha-32613';
+$wp_version = '4.3-alpha-32614';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.