* We actually have distlib 0.2.3 vendored
* Update colorama to 0.3.7
* Use unix line endings
* Upgrade requests to 2.10.0
* Upgrade pyparsing to 2.1.1
* Update pkg_resources to 21.0.0

We want the root logger to output debug level logs when we have
specified "--log".  The log-file handler then sends this to our file,
and the other handlers (console) filter out at their appropriate
level.

This restores the intended behaviour of "--log" argument, which is
supposed to output verbose logs to a file always.

A test-case is added

Closes: #3351

Closes #3638

* Drop markers inside InstallRequirement.check_if_exists

Any requirement that are checked if they are installed may specify
an environment marker. Since the marker may include information that
we no longer have context for (such as which extra requires that
requirement), and we have already decided that we are going to install
the requirement, drop the marker when we check if it's installed.

* Update pkg_resources from setuptools 20.7.0

* Update pkg_resources to setuptools 20.4, remove _markerlib

_markerlib was part of what we pulled in from setuptools and was
depended on by pkg_resources; it's totally gone from setuptools so
it can totally go here.

* Use packaging.markers to evaluate markers instead of distlib

* Update packaging to 16.7

Use logger.warning instead of deprecated logger.warn

Add more detail to the 'Multiple .dist-info directories' error

Make have_compatible_glibc more robust against unusual version strings

Give markers chance to remove incompat wheel links

`pip install -r reqs.txt` was failing when the requirements file includes
an unsupported wheel, regardless of whether it is conditionally removed
by a marker. This patch fixes that issue.

Additionally, this patch makes pip check local file wheels for
compatibility. Previously, a requirements file could include a path
to a valid wheel for any platform and pip would happily install it.

Fix crash on systems with uninitialized locale

locale.setlocale(locale.LC_ALL, '') apparently crashes in such case.
The raised exception can be safely ignored as locale loading is only
used to automatically detect the default encoding for requirements.txt
files.
Closes #3575

Update to packaging 16.6

Downstream forks/redistributors of glibc apparently sometimes add junk
onto the end of the version number -- e.g. Linaro glibc might have a
version number like "2.20-2014.11". This makes the glibc version number
parsing code ignore the rest of the string after the minor version
number, to be robust against Linaro's current usage, as well as whatever
exciting new weirdnesses that other redistributors might come up with
in the future.

Fixes: gh-3588

Packaging requirements

Fix req file encoding detection

Added missing space

Added a space missing in multi-line help text string.

Fix typo: Envionment -> Environment