add contract_sig field

src/exchangedb/common-0001.sql

@@ -1326,6 +1326,7 @@ BEGIN
       '(contract_serial_id BIGINT GENERATED BY DEFAULT AS IDENTITY' --UNIQUE
       ',purse_pub BYTEA NOT NULL CHECK (LENGTH(purse_pub)=32)'
       ',pub_ckey BYTEA NOT NULL CHECK (LENGTH(pub_ckey)=32)'
+      ',contract_sig BYTEA NOT NULL CHECK (LENGTH(contract_sig)=64)'
       ',e_contract BYTEA NOT NULL'
       ',purse_expiration INT8 NOT NULL'
       ',PRIMARY KEY (purse_pub)'

src/exchangedb/exchange-0001-part.sql

@@ -1068,6 +1068,8 @@ COMMENT ON TABLE contracts
   IS 'encrypted contracts associated with purses';
 COMMENT ON COLUMN contracts.purse_pub
   IS 'public key of the purse that the contract is associated with';
+COMMENT ON COLUMN contracts.contract_sig
+  IS 'signature over the encrypted contract by the purse contract key';
 COMMENT ON COLUMN contracts.pub_ckey
   IS 'Public ECDH key used to encrypt the contract, to be used with the purse private key for decryption';
 COMMENT ON COLUMN contracts.e_contract