Do menu and Utilities class>>#grabScreenAndSaveOnDisk

Hi all,

The "Do" menu has an item which I tried to use, but doesn't seem
available.  This is in Squeak 6.0a-#17799.

Utilities class>>#grabScreenAndSaveOnDisk

Seems useful.  Should it come back?

I have found an implementation of it in GIFReadWriter.  But: the example
in its method comment used an incorrect name for the class.  I have
fixed that and attached a change set.

(The GIF screenshot this method saves looks surprisingly good,
considering I'm on a display using millions of colors.)

Thanks,
Tim