Windows: avoid printing errors from filters.

Broke rclzip because of message going to stdout (why?).

src/filters/rclexecm.py

@@ -89,7 +89,10 @@ class RclExecM:
             self.errfout = sys.stderr
         
     def rclog(self, s, doexit = 0, exitvalue = 1):
-        print("RCLMFILT: %s: %s" % (self.myname, s), file=self.errfout)
+        # On windows, and I think that it changed quite recently (Qt change?)
+        # we get stdout as stderr. So don't write at all
+        if sys.platform != "win32":
+            print("RCLMFILT: %s: %s" % (self.myname, s), file=self.errfout)
         if doexit:
             sys.exit(exitvalue)