cmogstored 1.8.0

devXXX/usage files are emitted properly for systems where
the mount point can't be resolved.  This is needed for
multi-device filesystems such as btrfs.

PUT and DELETE requests now update the in-memory representation
of these devXXX/usage files, since the 10s update interval may
be too low for high-traffic situations.

Their is a new "USAGE FILES" section in the manpage documenting
the changes from 1.7.0 and this release.

Our public mail archives are now available over IMAPS.
gnulib is updated to 4e082bffbcc46e68 in the tarball.