Fsignal cleanup

[storm@cua.dk (Kim F. Storm)]

Following the recent confusion over whether Fsignal and wrong_type_argument
return or not, I went ahead and cleaned up this whole mess.

There is now a new function `xsignal' which is similar to `Fsignal',
but is guaranteed never to return.

To further clean up the code, I've added  functions xsignal0, xsignal1,
xsignal2, and xsignal3, which are like xsignal, but they take a fixed
number of arguments and build a list from those arguments which is
then passed on to xsignal.

Finally, I took the signal_error function from xfaces.c and generalized
it a bit to be useful everywhere we signal a Qerror with a string +
additional args.  The arg need not be a list; if not, it is automatically
made into a 1-element list before being passed to xsignal.

There are still calls to Fsignal left in the code.  Those all signal Qquit
-- which may return if the debugger says so.

-- 
Kim F. Storm <storm@cua.dk> http://www.cua.dk