tests/test-gendoc-sv.t

context: set stack level for deprecation warning

This patch makes the deprecation warning print the caller of
repo.__getitem__. That's not quite correct, since there could also be
other callers of changectx.__init__, but it seems like the most
helpful stack level in practice.

Differential Revision: https://phab.mercurial-scm.org/D3307

#require docutils gettext

  $ $TESTDIR/check-gendoc sv
  checking for parse errors