Reform the dialog special node types.

- Any picture type is now possible; the nodes split by picture type alone were merged
- Town portal now honours your chosen picture. Town stairway also allows you to choose.
- The two one-shot dialogs now use msg3 where they previously used msg2; this is to make way for later expansion

rsrc/strings/specials-text-town.txt

@@ -292,8 +292,8 @@ Unused
 Number of first message in dialog
 Unused
 Unused
-Terrain Picture number
-Unused
+Picture number
+Picture type
 Unused
 If Pulled, call this special ...
 Unused
@@ -308,8 +308,8 @@ Unused
 Number of first message in dialog
 Unused
 Unused
-Dialog Picture number
-Unused
+Picture number
+Picture type
 X coordinate to telep. to
 Y coordinate to telep. to
 Unused
@@ -324,8 +324,8 @@ Unused
 Number of first message in dialog
 Unused
 Unused
-Unused
-Unused
+Picture number
+Picture type
 X coordinate to place at
 Y coordinate to place at
 Unused