Fix libsepol/checkpolicy handling of ~self

[stephensmalley]

libsepol/checkpolicy do not presently handle ~self (including ~{ a b self }) correctly.
~ is only applied to the type set, not self, while self continues to be processed separately (without being complemented). We should either reject this as a syntax error in checkpolicy or handle it correctly in checkpolicy and libsepol.