profiling aufs

Ok,
    Here are my thoughts on the changes needed to use the hires
profiling on aufs:

1) during thread creation, or at the first prof_start in a new thread,
create a new profiling data block, and save the pointer in a) a global
list of profiling data blocks, and b) a pre-reserved pthread_key.
2) prof_start and prof_end use pthread_getspecific() to access the
thread specific data block.
3) prof_event merges the data from all the thread specific data blocks
into the accumlators.

Thoughts?

Will this add too much overhead for the profiling code to be still
effective in debugging? I don't think so, but am open to other
suggestions.

Oh, and if _REENTRANT is not defined, we only perform single-thread
profiling.

Rob