fix single quote escape for append, contains

[nixon]

revert back to fabric1 version of _escape_for_regex to handle single
quotes and other special characters.

also escaped double quotes in filename and added testcases.

refs #34

[nixon]

I also used this test script to make sure things were working outside the test mock environment:

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import tempfile

from invoke import Context
from fabric import task
from patchwork.files import append


@task
def testcases(c, fname):
    expected = [
        "alias l='ls -rtl'",
        'trailing $',
        'trailing $$',
        'an env var is not expanded: $HOME',
        "trailing single quote '",
        'trailing double quote "',
        'trailing backtick `',
        'backticks dont execute `id`',
        'no command substitution $(id)',
        '',  # an empty line
        'a single \\ backslash',
        'a single trailing backslash \\',
        "listen_addresses = '*'",
    ]

    for line in expected:
        append(c, fname, line)

    actual = open(fname).read().strip()

    assert actual == '\n'.join(expected), actual


def runtests():
    c = Context()

    with tempfile.NamedTemporaryFile() as f:
        testcases(c, f.name)
        testcases(c, f.name)


if __name__ == "__main__":
    runtests()

[nixon]

FWIW, I think the Travis failures are related to a recent semantic-version change. If I pin to semantic-version<2.7, then I don't get that ValueError: Call either Version('1.2.3') or Version(major=1, ...) anymore.