Virtually dispatched scavengers

Virtually dispatched scavengers

Use virtually dispatched specialized scavengers instead of single generic ScavengeObjectSlow implementation.

Rollback of r5041 with assertion checking callback alignment removed. Map space is iterated in a special fashion during scavenges so special callback alignment is not required.

Review URL: http://codereview.chromium.org/2950003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5047 ce2b1a6d-e550-0410-aec6-3dcde31c8c00