[Squeak-VMdev] [BUG][FIX] Linux 2GB problem in FFI

[Bert F. <be...@im...>]

This bug is similar to the image segment loading problem when the 
object memory spans the 2GB boundary. Ned has fixed that, but FFI uses 
the #isInMemory: method which was not fixed.

The attached changeset makes #startOfMemory return an unsigned value 
(just like endOfMemory, which Ned fixed), and casts the parameter of 
#isInMemory: to unsigned.

- Bert -