Fix build with GCC 4.4

Lubomir Rintel <lkundrak@v3.sk>

diff -up grass-6.3.0/imagery/i.atcorr/Output.h.gcc44 grass-6.3.0/imagery/i.atcorr/Output.h
--- grass-6.3.0/imagery/i.atcorr/Output.h.gcc44	2009-03-23 21:22:56.664618731 +0100
+++ grass-6.3.0/imagery/i.atcorr/Output.h	2009-03-23 21:23:10.349620131 +0100
@@ -4,6 +4,7 @@
 #include <iostream>
 #include <sstream>
 #include <string>
+#include <cstdio>
 
 class Output
 {