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.

cat: factor out a function that populates the formatter This will allow extensions to add data to the templater.

svnsubrepo: add new method _svnmissing This is modelled after _gitmissing from dea6efdd7ec4 and also necessary for svn. I'm not sure exactly how this hasn't been more of a problem for svn until now, actually.

svnsubrepo: decorate dirty method with annotatesubrepoerror This function invokes svn commands which can error out in any number of ways, so it's helpful to know in which subrepo this error happens.

match: do not weirdly include explicit files excluded by -X option Actually, this was the original behavior. Before a83a7d27911e, "log" and "files" showed nothing if "FILE -X FILE" was specified, whereas "debugwalk" got confused by an explicit FILE pattern. Under the hood, "log" and "files" use m() and ctx.matches(m) respectively, and "debugwalk" uses ctx.walk(m). I suspect dirstate.walk() goes wrong in _walkexplicit(), which seems to blindly trust m.files(). I reckon the original "log"/"files" behavior is correct, and drop the hack from the differencematcher.

lfs: add the '{oid}' template keyword to '{lfs_files}' The 'sha256:' prefix is skipped because this seems like the most convenient way to consume it. Maybe we should also add a '{oid_type}' keyword? Then again, that can be added in the future if a different algorithm is supported.

lfs: convert '{lfs_files}' keyword to a hybrid list This will allow more attributes about the file to be queried.