Made the style-check scripts send their file lists to stderr.

A complete list will be shown before make shows its error message.  There will be less confusion about which lines are in the list.

.github/checks/spaces.sh

@@ -10,9 +10,9 @@ FILES=`find $CHECK_PATH -type f \( -name \*.inc -o -name Makefile -o -name \*.cf
 cd $OLDCWD
 
 if [ x"$FILES"x != xx ]; then
-    echo "error: found dangling spaces in the following files:"
+    echo "error: found dangling spaces in the following files:" >&2
     for n in $FILES; do
-        echo $n
+        echo $n >&2
     done
     exit -1
 fi