More tests for Union & Intersect

Some fixes of corner cases on the way

R=bmeurer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/230923005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20684 ce2b1a6d-e550-0410-aec6-3dcde31c8c00