class_registry's staticness brings has the usual problem of
static classes (loss of dependency information) and prevents us
from librarifying Scylla since all objects that define a registration
must be linked in.
Take a first step against this staticness by defining a nonstatic
variant. The static class_registry is then redefined in terms of the
nonstatic class. After all uses have been converted, the static
variant can be retired.
Message-Id: <20181126130935.12837-1-avi@scylladb.com>
c6d700279b