Add dispatch_forever as a separate function with no timeout

[geky]

Unfortunately, with the recent addition of a type-infering callback function, the overloaded dispatch member function creates an ambiguity when passed to threads.

With dispatch_forever function, a thread for the event queue can be started simply like this:

t.start(&queue, &EventQueue::dispatch_forever);

Thanks to @bogdanm for the find/solution

[bogdanm]

:+1: