floor access

A post-3.4.3 change dealing with reaching into pits resulted in "you
sit on the air" if you used the #sit command after escaping a pit trap.
Change can_reach_floor() so that caller explicitly controls whether being
on the brink of a pit is a condition that prevents reaching the floor.
This also splits a fairly common message about not being able to reach the
floor into a separate routine.

     There is still oddness here:  if you're polymorphed into a flyer,
#sit yields "you sit down" followed by "you fly over a pit" (latter occurs
when escaping trap activation).  A ceiling hider behaves similarly, but
the second message is "you escape a pit" and doesn't sound quite as silly.
Perhaps #sit should pass TOOKPLUNGE to dotrap(), or maybe there's some
better way to handle this?

src/invent.c

@@ -1,4 +1,4 @@
-/*	SCCS Id: @(#)invent.c	3.5	2005/04/06	*/
+/*	SCCS Id: @(#)invent.c	3.5	2005/06/02	*/
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -2257,7 +2257,7 @@ boolean picked_some;
 		}
 		if (dfeature && !drift && !strcmp(dfeature, surface(u.ux,u.uy)))
 			dfeature = 0;		/* ice already identifed */
-		if (!can_reach_floor()) {
+		if (!can_reach_floor(TRUE)) {
 			pline("But you can't reach it!");
 			return(0);
 		}