Description:
------------
The xhprof tests related to timing fail on Mac OS X 10.7.2.

As already described here, simple test scripts do fail:

https://bugs.php.net/bug.php?id=58676

( See below )

This patch fixes the issue by using the provided mach timer apple framework:

https://developer.apple.com/library/mac/#qa/qa1398/_index.html

By using mach_absolute_time() and mach_timebase_info() the issue is fixed and the 
tests do pass on Mac OS X 10.7.2. (Sometimes they still fail, but before they had 
failed always).

Test script:
---------------
<?php

xhprof_enable();
sleep(3);
$raw = xhprof_disable();
var_dump($raw["main()"]["wt"]);

When I run this with your patch on Mac, a bunch of times, I expect to see walltime (wt) of about 3 Million microsecs. But the program prints fairly fluctuating numbers each time I run:

[apples-macbook-pro:~] Apple% $HOME/php/bin/php -dextension=xhprof.so test.php
int(1274841)
[apples-macbook-pro:~] Apple% $HOME/php/bin/php -dextension=xhprof.so test.php
int(2232810)
[apples-macbook-pro:~] Apple% $HOME/php/bin/php -dextension=xhprof.so test.php
int(1496259)

On Linux, we get numbers fairly close to 3000000 each time.

Expected result:
----------------
int(3000653)

It should be close to int(3000000).

Actual result:
--------------
int(1274841)