(export_p12_file): Read a certificate from STDIN and pass it to
p12_build. Detect a keygrip and construct the filename in that
case. Unprotcet a key if needed. Print error messages for key
formats we can't handle.
(release_passphrase): New.
(get_passphrase): New arg PROMPTNO. Return the allocated
string. Changed all callers.
* minip12.c: Revamped the build part.
(p12_build): New args CERT and CERTLEN.
* simple-pwquery.c (agent_open): Don't mangle INFOSTR.
* export.c (export_p12, popen_protect_tool)
(gpgsm_p12_export): New.
* gpgsm.c (main): New command --export-secret-key-p12.
