This improves our static type information by calculating the result type
of conversions (HChange) during range analysis. It allows e.g. to eliminate
the write barrier in the following example where it was not possible before:

function f(x) {
  var y = x + 1;
  if (y > 0 && y < 100) {
    a[0] = y;
  }
}


* Fix bug in Range::Copy. The minus-zero flags has to be preserved by default.
Review URL: http://codereview.chromium.org/7634022

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8994 ce2b1a6d-e550-0410-aec6-3dcde31c8c00