D5094: merge-tools: when calling external merge tool, describe the resolve inputs

[Yuya Nishihara]

>   >   class mappingdict(mappable, _mappingsequence):
>   >       """Wrapper for a single template mapping
>   >   
>   >       This isn't a sequence in a way that the underlying dict won't be iterated
>   >       as a dict, but shares most of the _mappingsequence functions.
>   >       """
>   >   
>   >       def __init__(self, mapping, name=None, tmpl=None):
>   >           super(mappingdict, self).__init__(name, tmpl)
>   >           self._mapping = mapping
>   >   
>   >       def tomap(self, context):
>   >           return self._mapping
>   >   
>   >       def tobool(self, context, mapping):
>   >           # no idea when a template mapping should be considered an empty, but
>   >           # a mapping dict should have at least one item in practice, so always
>   >           # mark this as non-empty.
>   >           return True
>   >   
>   >       def tovalue(self, context, mapping):
>   >           return super(mappingdict, self).tovalue(context, mapping)[0]
>   
>   I copy/pasted this to https://phab.mercurial-scm.org/D5211. :)

I sent my version with `{p1}/{p2}` example.

You don't need to update this series. I'll queue it once my patches are
accepted.