agent: Minor tweaks to the new genpin inquiry.

* agent/call-pinentry.c (generate_pin): Use STRING random which is
sufficient for a passphrase.
(inq_cb): s/rc/err/.  Do not print two errors in case generate_pin
fails.  Lowercase strings as per GNU standards.
(setup_genpin): Fix translation test.
(setup_qualitybar): Ditto.

Our policy is to use VERY_STRONG for a long term public key but not
for symmetric keys.

The GNU standards to demand that strings start with a lowercase
because that seems to be needed if it follows a prefix of for example
"gpg:". I don't actually like this becuase we need different strings
in interactive and standard mode but the majory of strings in GnuPGare
written this way. If a translation is necessary it can be done with
an en_GB or so locale.

• Signed-off-by: Werner Koch <wk@gnupg.org>