help dirmngr be more idle

[Daniel Kahn Gillmor]

A patch series follows that aims to help dirmngr tread more lightly on
the system it uses.  In particular, on my system, a default dirmngr
process wakes up twice every two seconds and then immediately goes
back to sleep.

This represents a potential problem for power management, and suggests
that there is room for improvement at least in the default case where
dirmngr is mostly idle.  This concern was raised quite some time ago
in the debian BTS, for example: https://bugs.debian.org/507361.

With these patches applied, an idle dirmngr is actually idle --
waiting in the kernel's select() for activity to wake it up.  It is no
less responsive to the user, and it doesn't burn CPU it doesn't need.

Comments welcome!

Regards,

        --dkg