[FIX] Query passphrase cache with secret key ID

- Before each public key encrypted packet key id was used
  to check against a list of public keys if such a public key
  exists and if it did, it was used to check against the passphrase
  cache, if the passphrase for that key was already in the cache.
  That doesn't make any sense at all, instead the list of secret keys
  has to be checked against the public key id.
Merge branch 'dev' of https://github.com/GPGTools/GPGMail into dev