Automatically choose between BlockingQueuedConnections and QueuedConnections

Currently it is very dangerous to pass non-const pointers and non-const references via a connection or via invokeMethod() to a slot - if the connection is (automatically) executed as a QueuedConnection the application will possibly crash if the called slot modifies the referenced object. However this would be totally safe if Qt would automatically choose between BlockingQueuedConnections and QueuedConnections: a connection should be BlockingQueued if any non-const pointer or non-const reference (or a return-value) is passed.