template: add ifcontains template function Adds a template function with the signature 'ifcontains(item, set, then[, else])'. It can be used to do things like '{ifcontains('.hgignore', file_mods, label(...), ...)}' to color commits that edit the .hgignore file. A future patch will add the revset() function which will combine with ifcontains to allow us to color commits if they are in the revset.

createmarkers: allow to pass metadata for a marker only The `metadata` argument only allow to specify metadata for all new markers. We extension the format of the `relations` argument to support optional metadata argument. The first user of this should be the evolve extension who want to store parent information of pruned changeset in extra (until we make a second version of the format)

obsstore: update create docstring to point to the coder friendly function The `obsstore` class have a `create` method that create new obsolescence marker from node. There is another function in the same module `createmarkers`. This other function is higher level and automatically missing meta data (ultimately calling the first one) We add a new comment in the docstring of `obsstore.create` highlighting that people writing new code probably want to use the top level one.

i18n: check equality of initial indentation between msgid and msgstr Document generation by runrst in "doc" directory may succeed silently, even though initial indentation is different between msgid and msgstr: for example, it may be unexpected or missing indentation. This patch adds the checker to check equality of initial indentation between msgid and msgstr. This checker is categorized as "warning" level, because problem detected by this is not so serious for usual Mercurial usage.