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.

src/files.c

@@ -1420,7 +1420,7 @@ docompress_file(filename, uncomp)
 const char *filename;
 boolean uncomp;
 {
-	gzFile *compressedfile;
+	gzFile compressedfile;
 	FILE *uncompressedfile;
 	char cfn[256];
 	char buf[1024];