differ: make basediff constructor public
differ: make basediff constructor public

Signed-off-by: Tonis Tiigi <c2470c48b2d3312d61f94f18d3a1cd113d1915ad@gmail.com>
estesp/containerd,vdemeester/containerd,thaJeztah/containerd,hqhq/containerd,mikebrow/containerd,mikebrow/containerd,rajasec/containerd,containerd/containerd,AkihiroSuda/containerd,miaoyq/containerd,estesp/containerd,miaoyq/containerd,containerd/containerd,chanezon/containerd,crosbymichael/containerd,dmcgowan/containerd,dmcgowan/containerd,vdemeester/containerd,crosbymichael/containerd,kunalkushwaha/containerd,kunalkushwaha/containerd,thaJeztah/containerd