Marking fake LeftAndMain->redirect() responses as finished

Introduce new LeftAndMain_HTTPResponse class for this purpose,
to mark a response as finished regardless of HTTP status.
This is required for ajax responses which do redirects on app layer
rather than HTTP (to avoid double processing).

Specifically required to decorate LeftAndMain->init()
in the 'translatable' module (TranslatableCMSMainExtension),
which marks the response as finished through its redirect,
avoiding further processing after init().

admin/code/LeftAndMain.php

@@ -358,6 +358,17 @@ function redirect($url, $code=302) {
 			if($this->request->getHeader('X-Pjax') && !$this->response->getHeader('X-Pjax')) {
 				$this->response->addHeader('X-Pjax', $this->request->getHeader('X-Pjax'));
 			}
+			$oldResponse = $this->response;
+			$newResponse = new LeftAndMain_HTTPResponse(
+				$oldResponse->getBody(), 
+				$oldResponse->getStatusCode(),
+				$oldResponse->getStatusDescription()
+			);
+			foreach($oldResponse->getHeaders() as $k => $v) {
+				$newResponse->addHeader($k, $v);
+			}
+			$newResponse->setIsFinished(true);
+			$this->response = $newResponse;
 			return ''; // Actual response will be re-requested by client
 		} else {
 			parent::redirect($url, $code);
@@ -1471,3 +1482,19 @@ function mark($node) {
 	}
 }
 
+/**
+ * Allow overriding finished state for faux redirects.
+ */
+class LeftAndMain_HTTPResponse extends SS_HTTPResponse {
+
+	protected $isFinished = false;
+
+	function isFinished() {
+		return (parent::isFinished() || $this->isFinished);
+	}
+
+	function setIsFinished($bool) {
+		$this->isFinished = $bool;
+	}
+
+}