engraving in inaccessible locations

Also from the newsgroup (2nd from "Three bugfixes for Xorns" [I got
the subject wrong on the previous spell of protection patch]):  when
phazing through walls or rock you could engrave as if it was ordinary
floor.  Again I didn't use the user's patch; it left closed doors, raised
drawbridge, and iron bars as locations where engraving was still feasible
and said "you can't write in solid rock" even if you were inside a tree.
[The 3rd of "3 xorn fixes" was for misleading feedback when attempting to
engrave while underwater; we've already fixed that one.]

     There was a suggestion that you should be able to engrave within solid
rock if you use a wand of digging, and that seems like a pretty good idea,
but the check for location comes before the check for writing instrument so
would be tricky to implement.

src/engrave.c

@@ -1,4 +1,4 @@
-/*	SCCS Id: @(#)engrave.c	3.5	2005/06/22	*/
+/*	SCCS Id: @(#)engrave.c	3.5	2006/12/06	*/
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /* NetHack may be freely redistributed.  See license for details. */
 
@@ -499,6 +499,10 @@ doengrave()
 	if(Is_airlevel(&u.uz) || Is_waterlevel(&u.uz)/* in bubble */) {
 		You_cant("write in thin air!");
 		return(0);
+	} else if (closed_door(u.ux, u.uy) || !accessible(u.ux, u.uy)) {
+		/* stone, tree, wall, secret corridor, pool, lava, bars */
+		You_cant("write here.");
+		return 0;
 	}
 	if (cantwield(youmonst.data)) {
 		You_cant("even hold anything!");