Using RB_BIGNUM_TYPE_P macro

[S-H-GAMELINKS]

RB_BIGNUM_TYPE_P macro is defined and used in bignum.c and math.c.
But, some code used RB_TYPE_P to check bignum type(like RB_TYPE_P(e, T_BIGNUM) code).

I think it better to these code using RB_BIGNUM_TYPE_P macro instead of RB_TYPE_P macro.