Suppress pruning of futile interpositions in Kyoto Shogi

Suppress pruning of futile interpositions in Kyoto Shogi

In horizon nodes check evasions through drops on unprotected squares were
pruned, based on the idea that the checking slider would simply capture
the piece to renew the check. In games with automatic promotion (such as
Kyoto an micro-Shogi) this capture would alter the piece type, so we cannot
be sure it woul renew the check. The auto-promotion is recognize from
'promoDrops', as these always seem to go together.