Only write /etc/hosts when necessary.

Without this patch, sshuttle 'restores' /etc/hosts even if it didn't
make any modifications to it. This can be confirmed by running without
--auto-hosts and confirming that the modification time of /etc/hosts
is unchanged while sshuttle is running, but is updated when sshuttle
exits (and a debug2() message is printed indicating the file is
written).

I'm not aware of the previous behavior causing problems. However,
writing an important file unnecessarily as root should be avoided.

sdnotify.py documentation

Include sshuttle version in verbose output.

Some bug reports include verbose sshuttle output but lack the version
that is being used. Including the sshuttle version in the output may
make it easier to handle future bug reports.

Add psutil as dependency in setup.py

Bump flake8 from 3.8.3 to 3.8.4

Bump pytest from 6.1.0 to 6.1.1

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.8.3 to 3.8.4.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.8.3...3.8.4)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [pytest](https://github.com/pytest-dev/pytest) from 6.1.0 to 6.1.1.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest/compare/6.1.0...6.1.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump pytest from 6.0.2 to 6.1.0

Bumps [pytest](https://github.com/pytest-dev/pytest) from 6.0.2 to 6.1.0.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest/compare/6.0.2...6.1.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bump pytest from 6.0.1 to 6.0.2

Bumps [pytest](https://github.com/pytest-dev/pytest) from 6.0.1 to 6.0.2.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest/compare/6.0.1...6.0.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Fix #494 sshuttle caught in infinite select() loop.

Bump attrs from 20.1.0 to 20.2.0

Improve detection of when the ssh process exits in both daemon and
foreground modes. Previously, sshuttle could infinite loop with 100%
cpu usage if the ssh process died. On machines that use suspend, the
ssh connection might not resume after wakeup. Now, this situation is
detected and sshuttle exits. The fix involves changing the return
value we check for when we call poll() and using a psutil function to
detect when the process exits if we are running sshuttle as a daemon.

Bumps [attrs](https://github.com/python-attrs/attrs) from 20.1.0 to 20.2.0.
- [Release notes](https://github.com/python-attrs/attrs/releases)
- [Changelog](https://github.com/python-attrs/attrs/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/python-attrs/attrs/compare/20.1.0...20.2.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Fix python2 server compatibility

Python2 ignores the byte string qualification (b’foo’)  but falls over for the combination rb for this regexp. Switching the qualification to br appears to fix this and works in both python2 and python3.

Fixed typo.

Fixes  #469. We replace python3 exclusive code with a check for python3 and a compatibility fix. Note that the switch from os.set_nonblocking to fcntl.fcntl in 98d052d1 (fixing #503) also fixes python2 compatibility.

Change license text to LGPL-2.1

Bump attrs from 19.3.0 to 20.1.0

Bumps [attrs](https://github.com/python-attrs/attrs) from 19.3.0 to 20.1.0.
- [Release notes](https://github.com/python-attrs/attrs/releases)
- [Changelog](https://github.com/python-attrs/attrs/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/python-attrs/attrs/compare/19.3.0...20.1.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

allow Mux() flush/fill to work with python < 3.5

Bump pytest-cov from 2.10.0 to 2.10.1

Bumps [pytest-cov](https://github.com/pytest-dev/pytest-cov) from 2.10.0 to 2.10.1.
- [Release notes](https://github.com/pytest-dev/pytest-cov/releases)
- [Changelog](https://github.com/pytest-dev/pytest-cov/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest-cov/compare/v2.10.0...v2.10.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Fixes: #503

Fix parse_hostport to always return string for host