fix for "pause -1" on Windows

[Allin C. <cot...@wf...>]

Tha attached patch fixes "pause -1" on MS Windows for current CVS.  
That is, loading a file containing this command no longer crashes 
wgnuplot.exe.  

It may not be the most elegant fix, but I'm reluctant to go deeper 
since the "pause" apparatus is rather complex, particularly on 
Windows.

-- 
Allin Cottrell
Department of Economics
Wake Forest University, NC