inventory overflow prompting

If someone manages to get three or more items with inventory "letter"
'#', compact inventory selection prompts to list "#-#" instead of showing
every #.  It isn't possible to selectively pick a particular one anyway,
so this doesn't affect player choices.

1 #:  Which item? [$#a-zA-Z]
2 #:  Which item? [$##a-zA-Z]
3 #:  Which item? [$#-#a-zA-Z]
4 or more #: same as 3.

     This doesn't address the fact that picking up enough boulders as a
giant might overflow the BUFSZ buffer getobj() uses to collect inventory
letters prior to calling compactify() on them.

src/invent.c

@@ -716,6 +716,15 @@ register char *buf;
 				ilet = buf[i1];
 				continue;
 			}
+		} else if (ilet == NOINVSYM) {
+			/* compact three or more consecutive '#'
+			   characters into "#-#" */
+			if (i2 >= 2 && buf[i2 - 2] == NOINVSYM &&
+			    buf[i2 - 1] == NOINVSYM)
+				buf[i2 - 1] = '-';
+			else if (i2 >= 3 && buf[i2 - 3] == NOINVSYM &&
+			    buf[i2 - 2] == '-' && buf[i2 - 1] == NOINVSYM)
+				--i2;
 		}
 		ilet2 = ilet1;
 		ilet1 = ilet;