Add a new bigroom variant "pillars"

Some variants have a bigroom variant called "Mines of Moria";
this one is very much that, but has several different arrangements
of the pillars.

sys/unix/NetHack.xcodeproj/project.pbxproj

@@ -1570,6 +1570,7 @@
 				"$(NH_DAT_DIR)/bigrm-10.lua",
 				"$(NH_DAT_DIR)/bigrm-11.lua",
 				"$(NH_DAT_DIR)/bigrm-12.lua",
+				"$(NH_DAT_DIR)/bigrm-13.lua",
 				"$(NH_DAT_DIR)/bigrm-2.lua",
 				"$(NH_DAT_DIR)/bigrm-3.lua",
 				"$(NH_DAT_DIR)/bigrm-4.lua",