[SUGOI] Refresh Sprite2s

Previously, loading a custom character with support for another mod's SPR2, then the mod that freeslots it, would discard the custom character's sprites entirely. A level pack adding a new frame would basically ask every custom character to add their own freeslot mechanism to support it. Now they simply have to supply the frames, and they'll get used whenever the SPR2 is freeslot'd at all.

Did this before doing !1749 (merged) ... without that, this is practically required, because characters get loaded before level packs just to avoid save issues. But even with that, this would still be helpful as it makes a lot less stuff reliant on load order.

EXE: srb2win_refresh-spr2.exe