Change isred to isblack for rbnode struct in common/rbtree/rbtree.h.
Add parent to rbnode struct in common/rbtree/rbtree.h.
Add node initialization in rbnode_alloc() in common/rbtree/rbtree.h.
Rename vsize parameter to psize for rbnode_alloc() in
common/rbtree/rbtree.h.
Move rbnode_alloc() implementation from common/rbtree/rbtree.h to
common/rbtree/rbtree.c.
Reformat rbnode_alloc() in common/rbtree/rbtree.c.
Add psize to rbnode struct in common/rbtree/rbtree.h.
Add rbnode_payload_write() to common/rbtree/rbtree.h.