Set headerCharset in EmailComponent.

Apply patch from 'Shota Watanabe', that sets headerCharset on CakeEmail
instances created from within EmailComponent.

Fixes #3398

lib/Cake/Controller/Component/EmailComponent.php

@@ -288,6 +288,7 @@ public function initialize(Controller $controller) {
 	public function send($content = null, $template = null, $layout = null) {
 		$lib = new CakeEmail();
 		$lib->charset = $this->charset;
+		$lib->headerCharset = $this->charset;
 
 		$lib->from($this->_formatAddresses((array)$this->from));
 		if (!empty($this->to)) {