Changed int64_t to PHYSFS_sint64.

Because apparently some strange compilers can't do int64_t...
Oh, and I forgot to include the header, but that is totally unrelated, I promise!

src/modules/filesystem/physfs/Filesystem.cpp

@@ -560,7 +560,7 @@ namespace physfs
 	int Filesystem::getLastModified(lua_State * L)
 	{
 		const char * filename = luaL_checkstring(L, 1);
-		int64_t time = PHYSFS_getLastModTime(filename);
+		PHYSFS_sint64 time = PHYSFS_getLastModTime(filename);
 		if (time == -1)
 		{
 			lua_pushnil(L);