wincap.h: Rename assitant to assistant throughout. wincap.cc: Ditto.

* devices.in (exists_console): Use fhandler_console::exists () rather than raw
test.
* devices.cc: Regenerate.
* fhandler.h (fhandler_console::exists): Define new function.
* fhandler_console.cc (fhandler_console::need_invisible): Use
fhandler_console::exists () rather than raw test.
* spawn.cc: Rename assitant to assistant throughout.
(child_info_spawn::worker): Simplify test for when to start a non-Cygwin
process in its own process group.  Just do it whenever we start a non-Cygwin
process.

winsup/cygwin/fhandler_console.cc

@@ -2371,7 +2371,7 @@ bool
 fhandler_console::need_invisible ()
 {
   BOOL b = false;
-  if (GetConsoleCP ())
+  if (exists ())
     invisible_console = false;
   else
     {