lib/synchronizer: Check txid from server against response content
lib/synchronizer: Check txid from server against response content

This is a paranoia measure to detect malcious servers. We commented it
out before because the check was slow but since then we added the
Transaction.txid_fast function which is acceptably fast, so we re-enable
this check.

fyookball/electrum,fyookball/electrum,fyookball/electrum