Add Support for optional paramter for an image handle to CLS

[SteveMcNeill]

Without having to redo a whole crap ton of old code to take the new parameter, this seems like the easiest way to implement the addition of a new parameter to CLS for an optional image handle.

Tested with the simple code below, which runs and works as expected, with no issues:

$Color:32
Screen _NewImage(640, 480, 32)
foo = _NewImage(480, 320, 32)

_Dest foo
Cls , Red
_Dest 0
Cls , Blue

'at this point, both screens should be colored and our Dest is the 640x480 screen
Cls , Green, foo
Sleep
_PutImage (0, 0), foo 'If the CLS worked, we should put a green screen on the blue one, instead of a red one.

[mkilgore]

As always, automated tests would be good :P Your example could pretty easily be turned into an automated image test like these PAINT ones I made.