localize button click routines

Keep state local into click_*() for routines relating to button clicks
than in global variables around frame.c and main.c

screen.h

@@ -46,6 +46,7 @@ extern void closescreen();
 extern Scrn * openscreen(char *, Window);
 extern void realizescreens();
 extern void screentoback();
+extern void click_screendepth(Scrn *s, Time time);
 
 void closescreen();
 Scrn *openscreen(char *deftitle, Window root);