Brief documentation on wAppIconFor() and wWindowFor().

Brief comment on what wAppIconFor() and wWindowFor() do, as it
may not be immediately obvious.

Given a raw X11 Window they will find the AppIcon (or WWindow,
respectively) associated with that window.  Thus they can map an
X11 object to a Window Maker internal object.

src/appicon.c

@@ -1018,6 +1018,7 @@ static void remove_from_appicon_list(WScreen *scr, WAppIcon *appicon)
 	appicon->next = NULL;
 }
 
+/* Return the AppIcon associated with a given (Xlib) Window. */
 WAppIcon *wAppIconFor(Window window)
 {
 	WObjDescriptor *desc;

src/window.c

@@ -141,6 +141,7 @@ static void appearanceObserver(void *self, WMNotification * notif)
 }
 
 
+/* Return the WWindow associated with a given (Xlib) Window. */
 WWindow *wWindowFor(Window window)
 {
 	WObjDescriptor *desc;