tests/test-gendoc-sv.t

zsh_completion: install as _hg not hg

The contrib/zsh_completion file itself says to name it _hg.

With a name like `hg`, if the user has a line like `autoload ${^fpath}/*(N-.:t)`
in their zshrc, it will create a shell function named `hg` that will hide the
actual hg command and make hg unusable.

Separately from that though, the underscore prefix makes it actually work. The
zsh man page states:

    The convention for autoloaded functions used in completion is that they
    start with an underscore

This does not seem to just be a "convention", though. With the ill-advised line
removed from my zshrc and the file named
`/usr/local/share/zsh/site-functions/hg` (without the underscore), these
completions did not seem to get loaded and the ones from the zsh installation
were loaded instead.  If I renamed them to be
`/usr/local/share/zsh/site-functions/_hg`, however, they were loaded.

I manually tested the above statement by starting a new zsh instance with the
file in `/usr/local/share/zsh/site-functions` with the following names:
- As `hg`, `which _hg_labels` did not show anything
- As `_hg`, `which _hg_labels` showed the expected function.

#require docutils gettext

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