GString has a richer set of string operations than QString.  It should
be preferred to QString except where we need a QObject or reference
counting.  We don't here.  Switch to GString, and put its richer
interface to use.

Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20201211171152.146877-3-armbru@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>