Change the hashset of getLineOfSight(), getTargetBlock() and ...

...getLastTwoTargetBlocks() to short

As all three of these methods currently use a HashSet that takes a Byte, it
is not possible to include block IDs greater than 127, as they would have
negative values, and thus be ignored by direct comparison, so we use a Short instead.

JIRA: https://bukkit.atlassian.net/browse/BUKKIT-3888