Spawn vehicles with the correct pitch and yaw. Fixes BUKKIT-4220

This commit makes it so that minecarts will spawn using the pitch and yaw
from the Location they were spawned with.  Minecarts support the full
range of pitch and yaw values.

Additionally, this commit makes it so that boats will spawn using the
correct yaw from the location they were spawned with.  Boats completely
ignore the pitch value, so it isn't set.