Fix spurious result claims in Spartan Chess

Fix spurious result claims in Spartan Chess

Fairy-Max sometimes sees phantom mates, where evasion is possible through
promotion to royalty. The possibility for this is now detected based on
presence of expendable royalty in the list of participating pieces,
and this is used to suppress loss claims. (Checking if promotion is
indeed possible is limited to presence of 2nd-rank Pawn.)
 In addition promotion to royalty is now rejected as illegal in variants
without expendable royalty.