Patched physfsrwops to compile against SDL 1.2 (thanks, Rob!).

(transplanted from 540be489d50f9fe29f1f517202b6a9d199f36a2a)

docs/CREDITS.txt

@@ -164,6 +164,9 @@ CMake fixes:
 Bug fixes,
     Rémi Verschelde
 
+Bug fixes:
+    Rob Loach
+
 Other stuff:
     Your name here! Patches go to icculus@icculus.org ...
 

extras/physfsrwops.c

@@ -32,10 +32,16 @@
 #endif
 
 #if !TARGET_SDL2
+#ifndef RW_SEEK_SET
 #define RW_SEEK_SET SEEK_SET
+#endif
+#ifndef RW_SEEK_CUR
 #define RW_SEEK_CUR SEEK_CUR
+#endif
+#ifndef RW_SEEK_END
 #define RW_SEEK_END SEEK_END
 #endif
+#endif
 
 #if TARGET_SDL2
 static Sint64 SDLCALL physfsrwops_size(struct SDL_RWops *rw)