Well, I'm running on 3.4 patched with this generic rb tree
implementation in the fair scheduler (although these are slightly
cleaned up, so I still need to boot this version to make sure there's no
last minute snafus).  So I finally settled on a mechanism for the
type-safety, even though it's a big macro (not my first choice), it's
the mechanism that works on all versions of gcc that still matter.

This is still preliminary.  I have a user-space test program (that just
compiles the rbtree.h in userspace) and a test module that I want to
refine to do profiling & stress tests so that performance can be easily
checked on various architectures & compilers.  So here's the outstanding
list:

* insert_near not finished (low priority)
* find_near not yet tested
* augmented not yet tested