Some gremlins in the range checking of scm_num2long_long,

        * num2integral.i.c (NUM2INTEGRAL): Under non-BIGMPZ_FITSP case,
        corrections to range check for signed numbers.

        * standalone/test-num2integral.c (test_long_long): Exercise
        out-of-range errors on various cases.
        (test_ulong_long): New function, split from test_long_long and
        similarly exercising out-of-range.