Fix a bug in int -> uint32 conversion for the C grades.
tests/Mmakefile:
tests/hard_coded/from_int_int32.{m,exp}:
tests/hard_coded/from_int_uint32.m:
Add the above tests.
tests/hard_coded/from_int_uint32.exp:
Expected output for machines with a 64-bit int type.
tests/hard_coded/from_int_uint32.exp2:
Expected output for machines with a 32-bit int type.
library/uint32.m:
Fix a bug in the definition of from_int/2. On machines where Mercury has
a 64-bit int type the conversion should succeed for inputs up to (and
including) UINT32_MAX.
