Add a missing `@since 3.9.0` to the PHPDoc for `wp_register_plugin_realpath()`.

See #16953, #27700.


git-svn-id: https://develop.svn.wordpress.org/trunk@28011 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/plugin.php

@@ -637,7 +637,11 @@ function plugin_basename( $file ) {
 /**
  * Register a plugin's real path.
  *
- * This is used in {@see plugin_basename()} to resolve symlinked paths.
+ * This is used in plugin_basename() to resolve symlinked paths.
+ *
+ * @since 3.9.0
+ *
+ * @see plugin_basename()
  *
  * @param string $file Known path to the file.
  * @return bool Whether the path was able to be registered.