rhg: internally, return a structured representation from hg cat The purpose of this change is to make it possible to support limited templating in `hg cat`, so we could print separators between files etc. The templating itself is not implemented yet, so this functionality is unused in `rhg cat`. However, in our fork of hg we're implementing a slightly different command `hg jscat` which makes use of this. So accepting this change will let us minimize the size of the patch we're maintaining on our side. Differential Revision: https://phab.mercurial-scm.org/D11679