Remove remaining other/1 errors.

src/json.json_lexer.m:
src/json.m:
	Add specific error_descs for the remaining case that were
	covered by the other/1 case.  Delete the other/1 case.

	In error messages involving numbers be clear that the digits
	involved are decimal.

tests/bad_exponent.{json,exp}:
tests/bad_signed_exponent.{json,exp}:
	New test cases.

tests/zinc_soln_sep.exp:
tests/bad_hex_digits.exp:
	Conform to the second change above.