tests/test-check-shbang.t

ui: add new config option for help text width

Before this patch, when printing help text using `hg help`, or `hg log -h`,
the output will wrap at 78 chars even if the user has a bigger terminal width
and there is no config option to change it, making the experience different
from the commonly used `man` tool.

This patch introduces a new config option `ui.textwidth`, which replaces the
hardcoded number. It's set to 78 by default to maintain compatibility. When
set to 0, `hg help` will behave more like `man`.

#require test-repo

  $ cd "`dirname "$TESTDIR"`"

look for python scripts that do not use /usr/bin/env

  $ hg files 'set:grep(r"^#!.*?python") and not grep(r"^#!/usr/bin/env python")'
  [1]

look for shell scripts that do not use /bin/sh

  $ hg files 'set:grep(r"^#!.*/bin/sh") and not grep(r"^#!/bin/sh")'
  [1]