now use the identical implementation from ../common/membuf.c.
* pksign.c (agent_pksign): Changed arg OUTFP to OUTBUF and use
membuf functions to return the value.
* pkdecrypt.c (agent_pkdecrypt): Ditto.
* genkey.c (agent_genkey): Ditto.
* command.c (cmd_pksign, cmd_pkdecrypt, cmd_genkey): Replaced
assuan_get_data_fp() by a the membuf scheme.
(clear_outbuf, write_and_clear_outbuf): New.
* membuf.c (put_membuf): Wipe out buffer after a failed realloc.