* bignum.c (integer_unpack_num_bdigits_small: Extracted from
  rb_integer_unpack.
  (integer_unpack_num_bdigits_generic): Ditto.
  (integer_unpack_num_bdigits_bytes): New function.
  (rb_integer_unpack): Use above functions.
  Return a Bignum for INTEGER_PACK_FORCE_BIGNUM evenwhen the result
  is zero.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41202 b2dd03c8-39d4-4d8f-98ff-823fe69b080e