guessing GPG_AGENT_INFO

[Nicholas Cole]

gpg-agent can tell whether gpg-agent is running, but if the
environment variable has not been properly set, there seems to be no
way to set it without killing the gpg-agent process and starting it
again.

Is there any way to correctly 'guess' the settings for the
GPG_AGENT_INFO variable (for the case where gpg-agent has been called
with --use-standard-socket)?

It is very slightly frustrating that gpg-agent can report that it can
connect to a gpg-agent daemon, and then be unusable when gpg tries to
call it.... :-)

Best,

Nicholas