tests/test-gendoc-sv.t

run-tests: make coverage work out of tree

Currently coverage fails when run on an out-of-tree extension since
run-tests.py tries to load sitecustomize.py from self._testdir, which is the
dir for the extension's tests.

Differential Revision: https://phab.mercurial-scm.org/D6960

#require docutils gettext

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