Buffer stops - don't allow minecart launch

[brasscrest]

Suggestion: Buffer stops should be considered solid blocks for the purpose of launching minecarts. It doesn't appear to work that way now. If a cart stops at a buffer stop on a power rail, powering the rail doesn't launch the cart. This isn't a problem for a cart occupied by a player, since the cart can just be nudged forward to launch it. But it makes buffer stops less useful for builds where the carts are used for transporting items rather than players, since the launch can't be easily automated.