(pgg-pgp5-encrypt-region, pgg-pgp5-decrypt-region)

(pgg-pgp5-encrypt-region, pgg-pgp5-decrypt-region)
(pgg-pgp5-encrypt-symmetric-region, pgg-pgp5-encrypt-symmetric)
(pgg-pgp5-encrypt, pgg-pgp5-decrypt-region, pgg-pgp5-decrypt)
(pgg-pgp5-sign-region, pgg-pgp5-sign): Add optional 'passphrase'
argument to all these routines, so the passphrase can be managed
externally and passed in to the system.
(pgg-pgp5-sign-region): Use new name of	pgg-add-passphrase-to-cache
function.