While these casts can be implemented by casting via uint, the resulting
code is less readable than code that uses direct casts.
library/uint32.m:
Add cast_from_uint16/1 and cast_to_uint16/1.
NEWS:
Announce the above additions.
tests/hard_coded/Mmakefile:
tests/hard_coded/uint32_uint16_casts.{m,exp}:
Add tests for the new casts.
