wireprotov2peer: properly format errors
formatrichmessage() expects an iterable containing dicts with
well-defined keys. We were passing in something else. This caused
an exception.
Change the code to call formatrichmessage() with the proper argument.
And add a TODO to potentially emit the proper data structure from
the server in the first place.
Differential Revision: https://phab.mercurial-scm.org/D4441
#require docutils gettext
$ $TESTDIR/check-gendoc fr
checking for parse errors