Use Process Name as Windows Group Identifier, less verbose and more

user-friendly than full bundle identifier alternative.

Author: rmottola

Source/x11/XGServerWindow.m

@@ -1,4 +1,3 @@
-
 /* XGServerWindows - methods for window/screen handling
 
    Copyright (C) 1999-2020 Free Software Foundation, Inc.
@@ -1942,8 +1941,9 @@ - (int) window: (NSRect)frame : (NSBackingStoreType)type : (unsigned int)style
   /*
    * Mark the window as the application with name & class so the WM can group it
    */
+  const char *procName = [[[NSProcessInfo processInfo] processName] UTF8String];
   classhint.res_name = generic.rootName;
-  classhint.res_class = generic.rootName;
+  classhint.res_class = (char *)procName;
   XSetClassHint(dpy, window->ident, &classhint);
 
   window->map_state = IsUnmapped;