contrib/tcsh_completion

hgdemandimport: disable on Python 3.5

The demand importer functionality isn't working at all on Python 3.5.
I'm not sure what's wrong.

Since it isn't working, let's disable it completely.

```
$ HGRCPATH= hyperfine -w 1 -r 50 -- "~/.pyenv/versions/3.5.9/bin/python ./hg version" \
  "HGDEMANDIMPORT=disable ~/.pyenv/versions/3.5.9/bin/python ./hg version"
Benchmark #1: ~/.pyenv/versions/3.5.9/bin/python ./hg version
  Time (mean ± σ):     163.7 ms ±   2.2 ms    [User: 148.5 ms, System: 15.7 ms]
  Range (min … max):   161.0 ms … 170.2 ms    50 runs

Benchmark #2: HGDEMANDIMPORT=disable ~/.pyenv/versions/3.5.9/bin/python ./hg version
  Time (mean ± σ):     164.3 ms ±   1.4 ms    [User: 148.2 ms, System: 16.6 ms]
  Range (min … max):   161.4 ms … 169.8 ms    50 runs
```

Differential Revision: https://phab.mercurial-scm.org/D7953

#
# tcsh completion for Mercurial
#
# This file has been auto-generated by tcsh_completion_build.sh for
# Mercurial Distributed SCM (version 1.7.5+157-8a220ae0b2ba)
#
# Copyright (C) 2005 TK Soh.
#
# This is free software; you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free
# Software Foundation; either version 2 of the License, or (at your
# option) any later version.
#

complete hg \
  'n/--cwd/d/' 'n/-R/d/' 'n/--repository/d/' \
  'C/-/( -R --repository \
    --cwd \
    -y --noninteractive \
    -q --quiet \
    -v --verbose \
    --config \
    --debug \
    --debugger \
    --encoding \
    --encodingmode \
    --traceback \
    --time \
    --profile \
    --version \
    -h --help)/' \
  'p/1/(add addremove annotate blame archive \
    backout bisect bookmarks branch branches \
    bundle cat clone commit ci \
    copy cp debugancestor debugbuilddag debugcheckstate \
    debugcommands debugcomplete debugdag debugdata debugdate \
    debugfsinfo debugignore debugindex debugindexdot debuginstall \
    debugpushkey debugrebuildstate debugrename debugrevspec debugsetparents \
    debugstate debugsub debugwalk diff export \
    forget grep heads help identify \
    id import patch incoming in \
    init locate log history manifest \
    merge outgoing out parents paths \
    pull push recover remove rm \
    rename move mv resolve revert \
    rollback root serve showconfig debugconfig \
    status st summary sum tag \
    tags tip unbundle update up \
    checkout co verify version)/'