Rewrite shops system to be more general

- Shops can now contain more than one type of item (for example, both mage and priest spells)
- Shops can now specify any talking portrait
- Healing options in a shop now have an info button giving a brief explanation (partly because it was easier than maintaining the exception)
- Additional healing option (not present in default healing shops): cure acid
- Acid is also no longer removed when you leave town or end combat (unless it's about to wear off)
- Always start shop mode with the scrollbar scrolled to the top
- Fix crash when entering an outdoor shop (and outdoor dialogue for that matter)
- Treasure generation system can now return junk items (treasure type 0), but only if explicitly requested; this is possible in shops but not with monsters since 0 means no loot

Dialog Engine:
- When setting a scrollbar's maximum, it now ensures the current position doesn't end up greater than the maximum

src/boe.locutils.cpp

@@ -13,6 +13,7 @@ location which_party_sec;
 
 extern short which_combat_type,current_pc;
 extern eGameMode overall_mode;
+extern eGameMode store_pre_shop_mode, store_pre_talk_mode;
 extern location center;
 extern cUniverse univ;
 
@@ -41,13 +42,33 @@ void take_explored(short i,short j) {
 bool is_out() {
 	if((overall_mode == MODE_OUTDOORS) || (overall_mode == MODE_LOOK_OUTDOORS))
 		return true;
-	else return false;
+	else if(overall_mode == MODE_SHOPPING) {
+		std::swap(overall_mode, store_pre_shop_mode);
+		bool ret = is_out();
+		std::swap(overall_mode, store_pre_shop_mode);
+		return ret;
+	} else if(overall_mode == MODE_TALKING) {
+		std::swap(overall_mode, store_pre_talk_mode);
+		bool ret = is_out();
+		std::swap(overall_mode, store_pre_talk_mode);
+		return ret;
+	} else return false;
 }
 
 bool is_town() {
 	if(((overall_mode > MODE_OUTDOORS) && (overall_mode < MODE_COMBAT)) || (overall_mode == MODE_LOOK_TOWN))
 		return true;
-	else return false;
+	else if(overall_mode == MODE_SHOPPING) {
+		std::swap(overall_mode, store_pre_shop_mode);
+		bool ret = is_town();
+		std::swap(overall_mode, store_pre_shop_mode);
+		return ret;
+	} else if(overall_mode == MODE_TALKING) {
+		std::swap(overall_mode, store_pre_talk_mode);
+		bool ret = is_town();
+		std::swap(overall_mode, store_pre_talk_mode);
+		return ret;
+	} else return false;
 }
 
 bool is_combat() {