Replace bintree with rbtree implementation

Replace bintree with rbtree implementation

The biggest flaw with the bintree is that they can easily become
unbalanced. For example, if X server maps the video card memory into
its address space as 1:1 mapping, running scan-pagemap can be really
slow. This is because reading the 1:1 mapping will generate horribly
skewed binary tree that resembles more closely a single direction
linked list. Replacing the simple binary tree implementation with the
red black tree can make full scan over five times faster.

Signed-off-by: Timo Kokkonen <kaapeli@itanic.dy.fi>