Bump the depth of variables in stack traces to 4.

Giving more context allows developer to look at request/response data
more easily.

Fixes #5005

lib/Cake/View/Elements/exception_stack_trace.ctp

@@ -45,7 +45,7 @@ App::uses('Debugger', 'Utility');
 		if (!empty($stack['args'])):
 			foreach ((array)$stack['args'] as $arg):
 				$args[] = Debugger::getType($arg);
-				$params[] = Debugger::exportVar($arg, 2);
+				$params[] = Debugger::exportVar($arg, 4);
 			endforeach;
 		endif;