port the RBT code to userland by making it part of libc.

port the RBT code to userland by making it part of libc.

src/lib/libc/gen/tree.c is a copy of src/sys/kern/subr_tree.c, but with
annotations for symbol visibility. changes to one should be reflected
in the other.

the malloc debug code that uses RB code is ported to RBT.

because libc provides the RBT code, procmap doesn't have to reach into
the kernel and build subr_tree.c itself now.

mild enthusiasm from many
ok guenther@