Completion of previous patch. Negative number were denied
as the second argument to NAME_CONST.


mysql-test/r/func_misc.result:
  Bug#30832 completion: test result
mysql-test/t/func_misc.test:
  Bug#30832 completion: test case
  added negative numbers
sql/item_func.h:
  Bug#30832 completion
  The function that represents unary minus is considered a constant if the argument is.