SW: Add the currently unused InterpolateSO option.

A known issue, which also applies to existing settings like the voxel
toggle, is that its value gets written to the saved game, and when such
a game is loaded, the its value gets overwritten by the one in the
saved game. Options should move to settings.cfg later, anyway.

source/sw/src/game.cpp

@@ -210,7 +210,7 @@ const GAME_SET gs_defaults =
 {
     2, // border
     0, // border tile
-
+	TRUE, // interpolate sector objects
 // Network game settings
     0, // GameType
     0, // Level

source/sw/src/settings.h

@@ -33,6 +33,7 @@ typedef struct
 {
     int8_t BorderNum;
     int8_t BorderTile;	// Network only - disabled
+    SWBOOL InterpolateSO;
 // Net Options from Menus
     uint8_t NetGameType;   // 0=DeathMatch [spawn], 1=Cooperative 2=DeathMatch [no spawn]
     uint8_t NetLevel;      // 1-28