Bootstrap/Load: Include Plugin API via `require_once`

Currently, auto-prepended files need to directly modify the globals in order to add filters and actions. This is a bad idea. Globals are bad. You should never directly interact with the Plugin globals.

Fixes #37707.


Built from https://develop.svn.wordpress.org/trunk@38282


git-svn-id: http://core.svn.wordpress.org/trunk@38223 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/plugin.php

@@ -14,6 +14,8 @@
  * Also see the {@link https://codex.wordpress.org/Plugin_API Plugin API} for
  * more information and examples on how to use a lot of these functions.
  *
+ * This file should have no external dependencies.
+ *
  * @package WordPress
  * @subpackage Plugin
  * @since 1.5.0

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.7-alpha-38281';
+$wp_version = '4.7-alpha-38282';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-settings.php

@@ -20,7 +20,7 @@ define( 'WPINC', 'wp-includes' );
 // Include files required for initialization.
 require( ABSPATH . WPINC . '/load.php' );
 require( ABSPATH . WPINC . '/default-constants.php' );
-require( ABSPATH . WPINC . '/plugin.php' );
+require_once( ABSPATH . WPINC . '/plugin.php' );
 
 /*
  * These can't be directly globalized in version.php. When updating,