Fix for zsh signal problems with Slakware

["Seth M. LaForge" <sethml@xxxxxxxxxxxxxxxx>]

Under newer versions of slakware, zsh has the really annoying habit of
totally freezing whenever a child process gets a signal.  I've finally
found the cause.

The problem is that zsh tries to generate signames.h, a list of signal
names, from /usr/include/linux/signal.h.  In recent releases of
slakware, /usr/include/linux/signal.h consists solely of 
#include <asm/signal.h>.  Thus signames.h contains no signal names,
and zsh runs off the end of the signal name array when trying to look
up a signal name.

The solution: change lines 357-360 (in 2.6-beta10) of configure.in
from:

for SIGNAL_H in /usr/include/bsd/sys/signal.h   dnl Next
                /usr/include/linux/signal.h     dnl Linux
                /usr/include/sys/signal.h       dnl Almost everybody else
                /dev/null;                      dnl Just in case we fall through

to:

for SIGNAL_H in /usr/include/bsd/sys/signal.h   dnl Next
                /usr/include/asm/signal.h       dnl Newer Linux
                /usr/include/linux/signal.h     dnl Linux
                /usr/include/sys/signal.h       dnl Almost everybody else
                /dev/null;                      dnl Just in case we fall through

It would be even better to also have configure spit out an error if it
cannot find a signal.h which actually has some signals defined, but
that's a little more work.

This problem is also present in 2.5.03, and the fix should be the
same.

Seth