Make vasm cloadq be 3-address form.

Summary: cloadq{} as currently defined, is unsound; it conditionally loads
a value, which means it conditionally sets its dst register.
However, all instructions with a dest are assumed to always
set their dest. This broke two separate ways as I was doing other
things on top of master.

Reviewed By: @swtaarrs

Differential Revision: D1555363
Xdebug cleanup and trivial features

Summary: This PR performs cleanup and finishes all the the trivial features (the ones not discussed in #3704).

Additions:
* Implemented `xdebug_break()` function
  * This is similar to `hphpd_break()`, except for xdebug. Call this to cause a breakpoint
* Implemented `xdebug_disable()`, `xdebug_enable()`, and `xdebug_is_enabled()`.
  * These just manipulate the `DefaultEnable` ini setting underneath
* Implemented `xdebug_get_stack_depth()`
* Implemented `force_error_reporting` ini setting
  * This is a bitmask that will be ORed with the error reporting level to produce the final error reporting level
  * Implemented by creating corresponding hhvm runtime option `Log.ForceErrorReportingLevel`
* Implemented `halt_level` ini setting
  * This is a bitmask of error constants. The corresponding errors will be upgraded to `E_USER_ERROR` when encountered
  * Implemented by creating corresponding hhvm runtime option `ErrorHandling.UpgradeLevel`
* Implemented `scream` ini setting
  * This turns off the silencer
Closes https://github.com/facebook/hhvm/pull/3706

Reviewed By: @paulbiss

Differential Revision: D1544220

Pulled By: @sgolemon
Better error on "public void function"

Reviewed By: @jwatzman

Differential Revision: D1556218
Only show per-page details if --verbose passed

Summary: With --verbose, no change in output. Without:

```
**********************
** 2014-09-15 20:54:29
** Collecting results
{
    "Combined": {
        "HHVM CPU instructions": 78138995.592529,
        "HHVM CPU usec": 40209.838134254,
        "HHVM wall usec": 106544.9338731,
        "HHVM requests": 31001,
        "Siege requests": 30968,
        "Siege wall sec": 0.12,
        "Siege RPS": 517.77,
        "Siege successful requests": 29508,
        "Siege failed requests": 0,
        "Nginx hits": 31029,
        "Nginx avg bytes": 29601.767024397,
        "Nginx avg time": 0.11496248670598,
        "Nginx 200": 28210,
        "Nginx 499": 33,
        "Nginx 301": 1324,
        "Nginx 404": 1462
    }
}

**********************
** 2014-09-15 20:54:30
** All done
```

Reviewed By: @​aravind

Differential Revision: D1556256