lazycat-daemon/host-list.scm (host-list-rem-host): Improve

* lazycat-daemon/host-list.scm (host-list-rem-host): Improve error
  checking.
common/message.scm: Simplify conditionals

* common/message.scm (message-serialize)
  (message-set-error-flag!, message-set-request-flag!): Simplify
  conditionals: Use `or' instead of `if' where it's possible.