UIO: Make uio_copy_n single buffered.

This is a temporary solution. Should be refactored at
the same time as uio_copy.
UIO: Refactor uio_copy_while.
UIO: Test result range, not input ranges.
UIO: Make ascending input memory const.
UIO: Add test for uio_copy_while.
FORTY: Refactor handle_* procedures.
FORTY: Lengthen test text size (since buffers did)