Allow modifying movement speed, jump height and gravity per-player via the Lua API.

src/player.cpp

@@ -71,6 +71,11 @@ Player::Player(IGameDef *gamedef):
 	movement_liquid_fluidity_smooth = 0.5 * BS;
 	movement_liquid_sink = 10 * BS;
 	movement_gravity = 9.81 * BS;
+
+	// Movement overrides are multipliers and must be 1 by default
+	physics_override_speed = 1;
+	physics_override_jump = 1;
+	physics_override_gravity = 1;
 }
 
 Player::~Player()