Respect app.disable_push_state in DefaultLocationProxy.
Respect app.disable_push_state in DefaultLocationProxy.

Code paths dependent on the HTML5 history API were not all checking for
the disable_push_state flag, making it impossible to downgrade
history-compliant browsers for testing. Added disable_push_state check
in relevant code paths.

Moykn/sammy,quirkey/sammy,quirkey/sammy,Moykn/sammy,Moykn/sammy,cardil/sammy,cardil/sammy,cardil/sammy