When receiving a HEAD request, die() right before we start outputting content.

* Content doesn't make sense for HEAD requests
* Saves wear and tear on the server
* Introduces a filter: exit_on_http_head (we send TRUE through it)

fixes #14348. props mbijon, mitchoyoshitaka.

git-svn-id: https://develop.svn.wordpress.org/trunk@22347 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/template-loader.php

@@ -6,6 +6,14 @@
 if ( defined('WP_USE_THEMES') && WP_USE_THEMES )
 	do_action('template_redirect');
 
+/**
+ * Halt template load for HEAD requests. Performance bump by eliminating output
+ *
+ * @since 3.5.0
+ */
+if ( 'HEAD' === $_SERVER['REQUEST_METHOD'] && apply_filters( 'exit_on_http_head', true ) )
+        exit();
+
 // Process feeds and trackbacks even if not using themes.
 if ( is_robots() ) :
 	do_action('do_robots');