Profiler performance improvement

[Rik]

11/12/14

All,

I committed a patch from Julien Bect which removes most of the overhead of
profiling when it is not enabled
(http://hg.savannah.gnu.org/hgweb/octave/rev/91cd85a75705).

There was a roughly 200% slowdown from 3.4.X to the current development
branch.  This patch recovers about 60% of that.  And if I use
--disable-atomic-refcounts I get another 100% back.  This still leaves
about 40% of miscellaneous cruft.

--Rik