Allow spying on methods

Now that Pinkerton now depends on ext-uopz, it's trivial to extend
Pinkerton to spying on both static and instance methods, regardless of
their visibility.

Rather than use the Jasmine-like `spyOn($class, $method)` syntax, use the
more PHP-like `spyOn(array($class, $method))`.
Support methods specified with a class instance