bignum.c: use RB_INTEGER_TYPE_P
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56535 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
bignum.c: use RB_INTEGER_TYPE_P
macro RB_INTEGER_TYPE_P instead of combination of FIXNUM_P and
RB_BIGNUM_TYPE_P.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56535 b2dd03c8-39d4-4d8f-98ff-823fe69b080e