Make WALLIFIED_MAZE into a level flag.

It should now be randomly disabled for a 3rd of Gehennom, to make things
a tad more interesting there. It's also disabled in Baalzebub's lair,
to make things a little more interesting.

Still don't know why the beetle is disappearing.

util/lev_comp.l

@@ -296,6 +296,7 @@ shroud		{ savetoken(yytext); yylval.i=SHROUD; return FLAG_TYPE; }
 graveyard	{ savetoken(yytext); yylval.i=GRAVEYARD; return FLAG_TYPE; }
 icedpools	{ savetoken(yytext); yylval.i=ICEDPOOLS; return FLAG_TYPE; }
 solidify	{ savetoken(yytext); yylval.i=SOLIDIFY; return FLAG_TYPE; }
+corrmaze        { savetoken(yytext); yylval.i=CORRMAZE; return FLAG_TYPE; }
 [0-9]+d[0-9]+	{ char *p = strchr(yytext, 'd');
 		  savetoken(yytext);
 		  if (p) {

util/makedefs.c

@@ -1367,9 +1367,6 @@ static const char *build_opts[] = {
 #ifdef VISION_TABLES
 		"vision tables",
 #endif
-#ifdef WALLIFIED_MAZE
-		"walled mazes",
-#endif
 #ifdef ZEROCOMP
 		"zero-compressed save files",
 #endif