teetering on edge of pit

- when you're teetering on the edge of a pit you can use '>' to enter the pit
- pull the numerious teetering checks into a new function

include/extern.h

@@ -2088,6 +2088,7 @@ E boolean NDECL(unconscious);
 E boolean NDECL(lava_effects);
 E void FDECL(blow_up_landmine, (struct trap *));
 E int FDECL(launch_obj,(SHORT_P,int,int,int,int,int));
+E boolean FDECL(uteetering_at_seen_pit, (struct trap *));
 
 /* ### u_init.c ### */