Add setInput function to CakeRequest

Modify data originally from `php://input`. Useful for altering json/xml
data in middleware or DispatcherFilters before it gets to
RequestHandlerComponent or other controllers.

lib/Cake/Network/CakeRequest.php

@@ -915,6 +915,17 @@ public function input($callback = null) {
 		return $input;
 	}
 
+/**
+ * Modify data originally from `php://input`. Useful for altering json/xml data
+ * in middleware or DispatcherFilters before it gets to RequestHandlerComponent
+ *
+ * @param string $input A string to replace original parsed data from input()
+ * @return void
+ */
+	public function setInput($input) {
+		$this->_input = $input;
+	}
+
 /**
  * Allow only certain HTTP request methods. If the request method does not match
  * a 405 error will be shown and the required "Allow" response header will be set.