1. Fix an abort in the MLDS backend involving switches on uints.
2. Make string.string/1 handle uints.
compiler/ml_switch_gen.m:
Handle uints properly in a spot.
library/string.to_string.m:
Make string.string/1 handle uint values.
tests/hard_coded/Mmakefile:
tests/hard_coded/uint_switch_test.{m,exp}:
Add a test case.
