describe valset sorting according to v0.34 requirements (#169)

spec/core/data_structures.md

@@ -374,7 +374,8 @@ block.ValidatorsHash == MerkleRoot(state.Validators)
 
 MerkleRoot of the current validator set that is committing the block.
 This can be used to validate the `LastCommit` included in the next block.
-Note the validators are sorted by their voting power before computing the MerkleRoot.
+Note that before computing the MerkleRoot the validators are sorted 
+first by voting power (descending), then by address (ascending).
 
 ### NextValidatorsHash
 
@@ -385,7 +386,9 @@ block.NextValidatorsHash == MerkleRoot(state.NextValidators)
 MerkleRoot of the next validator set that will be the validator set that commits the next block.
 This is included so that the current validator set gets a chance to sign the
 next validator sets Merkle root.
-Note the validators are sorted by their voting power before computing the MerkleRoot.
+Note that before computing the MerkleRoot the validators are sorted 
+first by voting power (descending), then by address (ascending).
+
 
 ### ConsensusHash