Pack GlobalHandles::Node::state_ and three flags into uint8_t

TEST=test-api.cc (ApiObjectGroupsCycle, ApiObjectGroupsCycleForScavenger, IndependentWeakHandle)

Review URL: https://codereview.chromium.org/11875015
Patch from Kentaro Hara <haraken@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13383 ce2b1a6d-e550-0410-aec6-3dcde31c8c00