Add hallucinatory trap names

This adds many funny, realistic, and nonsensical traps to the game, to
be shown when the player is hallucinating.

Architecturally, the biggest change is merging the what_trap macro and
the "defsyms[trap_to_defsym(ttyp)].explanation" pattern into a single
function "trapname", which returns the name of the trap, handling the
hallucination case. There is also a second parameter used for overriding
hallucination in the occasional cases where the actual trap name should
always be returned.

In addition, the what_trap and random_trap macros are now obsolete and
not used anywhere, so they are removed.

src/cmd.c

@@ -2293,7 +2293,7 @@ int final;
             Strcpy(predicament, "trapped");
             if ((t = t_at(u.ux, u.uy)) != 0)
                 Sprintf(eos(predicament), " in %s",
-                        an(defsyms[trap_to_defsym(t->ttyp)].explanation));
+                        an(trapname(t->ttyp, FALSE)));
         }
         if (u.usteed) { /* not `Riding' here */
             Sprintf(buf, "%s%s ", anchored ? "you and " : "", steedname);