TLSF redux

[Tim]

Hi all

I wanted to share some thoughts about the best way to include TLSF in
RTEMS.

Initially, I inserted TLSF at the libc heap level - calls to malloc et
al would in turn call tlsf versions of these calls. Everything works
fine.

After this, I decided that inserting TLSF at the super-core level, _all_
heaps (including the libc heap) would gain reap the benefits
automatically. This proved a little messy, as I allowed each heap
_instance_ to choose whether it used TLSF or not. This is because a TLSF
control structure is currently ~3kB, and I felt that enforcing this
overhead would curb acceptance. This method also works fine.

I've also created a configure option that specifies whether the libc
heap uses TLSF or not.

Before I submit the patch to the list, I want to make sure it's
something everyone can live with, or without (via configure