Fix free list node ending up on evacuation candidate.

Fix free list node ending up on evacuation candidate.

This is a temporary fix which avoids compaction when incremental marking
is restarted during an old-space-step. That could turn the page that
holds the chosen free list node into an evacuation candidate. It could
also cause several other inconsistencies if it happens during scavenge.

R=vegorov@chromium.org

Review URL: http://codereview.chromium.org/8228010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9585 ce2b1a6d-e550-0410-aec6-3dcde31c8c00