We used to have a linked list of nodes that were internally
block-allocated.

I kept the node blocks and put them on two lists: 1) the list of all
allocated blocks, 2) the list of blocks with used nodes. (1) is used
to reclaim blocks and (2) is used for traversal during GC. To make
traversal on scavenges faster the nodes holding new space objects are
grouped in an auxiliary array.

This changes the minimal memory usage from 5 words per global handle
to 4. Additional word is used for new space handles.

Review URL: http://codereview.chromium.org/7054072

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8186 ce2b1a6d-e550-0410-aec6-3dcde31c8c00