sm: Ask for the password for password based decryption (pwri)

* sm/decrypt.c (pwri_decrypt): Add arg ctrl.  Ask for passphrase.
* sm/export.c (export_p12): Mark string as translatable.
* sm/import.c (parse_p12): Ditto.

This is finishes the support for PWRI.

The N_() marks are added so that we don't rely of the side-effect of
having the same strings in protect-tool.c

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