Optimize mail reinjection

- Mark reinjected mails so that Husk can shortcut the processing.
- Fix Cargo.toml to correctly include the patched version of
  sequoia-cert-store and sequoia-keystore.

src/mail.rs

@@ -87,7 +87,7 @@ pub async fn smtp_inject(from: String, to: &Vec<Recipient<'_>>, header: CHeader,
         rcpts.push(rcpt.try_into()?);
     }
 
-    let my_id = ClientId::Domain("husk.reinject".to_owned()); // TODO: add secret token?
+    let my_id = ClientId::Domain(defaults::HELO_REINJECT_ID.to_owned()); // TODO: add secret token?
     joinset.spawn(async move {
 
         // XXX