Drop free method of imageObj class

[sgillies@…]

It's no longer needed and is confusing users who should instead delete or
undef the image or let their interpreter's garbage collector get it.

[sdlime]

When did you make the change to the class destructor? If it was since 4.0 then 
I think we should change the free method to do nothing, but leave it in place. 
Otherwise scripts will break in a bad way. I'd rather see "class not found" 
messages than seg faults. Then for 4.3/4.4 we should remove it altogether.

Steve

[sgillies@…]

imageObj.free() is gone in 4.3.  Does nothing in 4.2, and I have
also brought attention of the change to leading Perl users.