conf: New option --show-socket.

* tools/gpgconf-comp.c (gc_component_t): Move this enum to ...
* tools/gpgconf.h: here.
* tools/gpgconf.c (oShowSocket): New.
(opts): Add new option.
(main): Implement new option.

This is a convenience options for software which directly connects to
gpg-agent and thus needs to new the socket. By using --show-socket
along with --launch that software can also autostart the agent or the
dirmngr. Without this two calls to gpgconf would be required.

Actually the same behaviour can be achieved by running
gpg-connect-agent to query the running gpg-agent's socket via GETINFO.
The gpg-connect also makes sure that the agent is started. This is
not anymore suggested because gpgconf shall in future be used for all
such things.

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