Fixed casting Closure to Array

Summary: When casting an object of type Closure to an Array, the result should be an array containing the closure.
This diff also fixes incorrect var_dump output for Closure to make the test pass.

Fixes #2918

Reviewed By: @ptarjan

Differential Revision: D1391371
Fix /stop when bind fails, redux

Summary: Third attempt at fixing this problem.  The IP and AdminPassword are missing in the stop url.  This causes a 60 second delay starting a new HHVM as it waits to kill based on the pidfile.

Added a callback class 'ServerEventListener' which gets a call when a server is about to close the listening socket.  HttpServer uses this callback to remove the pidfile.  The timing of removing the pidfile is sensitive as we have to remove it before a new HHVM thinks it created it.

Fixing this now in the context of a mysterious startup crash that happens when devs get impatient and restart the server multiple times. t4483583

Reviewed By: @bertmaher

Differential Revision: D1377159
Unclown mustache test

Summary: Should be reliable with per-run tempdirs

Reviewed By: @JoelMarcey

Differential Revision: D1398401