* src/assuan-defs.h (struct assuan_context_s): Add new flags,
in_inq_cb and confidential_inquiry.
* src/client.c (assuan_transact): Use the new flags to wipe the
outbound buffer for inquiry when CONFIDENTIAL.
* src/context.c (assuan_set_flag): When ASSUAN_CONFIDENTIAL is set in
inquire callback, set the confidential_inquiry flag.