lfs: allow the pointer file to be viewed with `hg cat -T '{rawdata}'` The only other interface to this data is `hg debugdata`, which requires knowledge of the filelog revision that corresponds to the changeset. Since the data is uninterpreted, this is an important debugging capability, and needs to be simpler to use than that. For non-LFS files, this displays the regular data. Alternately, we could forego the messy function extraction in the last patch if this template keyword can just be added unconditionally.