* bignum.c (big2ulong): Add code specialized for SIZEOF_LONG <=
  SIZEOF_BDIGITS.
  This prevents shift witdth warning from "num <<= BITSPERDIG".



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41615 b2dd03c8-39d4-4d8f-98ff-823fe69b080e