Add support for multiple metric groups to gmetric

This brings gmetric into line with Ganglia python modules which
already support comma-separated groups in metric descriptors.
Merge pull request #69 from satterly/feature/gmetric-groups

Add support for multiple metric groups to gmetric
Remove diskusage module from RPM building and disable multicpu by default
Forgotten glob change
Use err_ functions instead of perror(3)

Error messages from perror don't end up in syslog, but instead
they sometimes gets written over the RRD files, corrupting them.
Printf format string fixes
Merge pull request #71 from pabl0/minorbug

Minor bug fixes (perror)
Change metric name memory allocation.
Change metric->name's memory pool from host->pool to metric->pool.
Adjust metric name.
Merge pull request #72 from wartime/master

Fix issue "stale metric can't be deleted."
Merge branch 'master' into feature/gmetad-walk-hosts
Define gmetad config options