[ns] 2.1b8a Linux performance patch

[Tom Kelly <ctk21@cam.ac.uk>]

I've updated my performance patch to work with 2.1b8a and is available
from:
http://www-lce.eng.cam.ac.uk/~ctk21/code/

I noticed that the default ns-allinone-2.1b8a has validation failures on
my Pentium III, Linux 2.2.17, egcs-2.91.66, RH6.2 machine. These seem to
be due to the use of -O2 being used by default causing IEEE754 floating
point incompatibilities. This is fixed by the patch.

Hope it helps,
Tom