agent: When the password cache is cleared, also clear the ext. cache.
* agent/agent.h (agent_clear_passphrase): New declaration. * agent/call-pinentry.c (agent_clear_passphrase): New function. * agent/command.c (cmd_clear_passphrase): Call agent_clear_passphrase.
- Signed-off-by: Neal H. Walfield <neal@g10code.com>