This is patch 2673214 from mmadia. It is correct, since we unconditionally
include signal.h in many other places, and only sometimes include sys/signal.h.
It is necessary to compile on Haiku, I'm told.
svn:r1228
a) this is 2009
b) niels and nick have been comaintainers for a while
c) saying "all rights reserved" when you then go on to explicitly
disclaim some rights is sheer cargo-cultism.
svn:r1065