* bignum.c (bary_unpack_internal): Return -2 when negative overflow.
  (bary_unpack): Set the overflowed bit if an extra BDIGIT exists.
  (rb_integer_unpack): Set the overflowed bit.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41494 b2dd03c8-39d4-4d8f-98ff-823fe69b080e