* Uses the same generation method as the built in tmpdir, simply
  returns a different object type.

Cmds {install,wheel} should return proper error code

The `pip` executable was returning a successful status code (`0`) when
trying to install new packages with existing previous build directories.

Conflicts:
	tests/functional/test_install_cleanup.py
	tests/functional/test_wheel.py

The `pip` executable was returning a successful status code (`0`) when
trying to install new packages with existing previous build directories.

Refactor tests.lib.* to simplify and remove global state

we'll assume '_' means '-' in versions from wheel filenames

Writing bytecode can mess up the detection of updated files and
directories

This reverts commit 47faefcd.

* Move virtualenv creation out of TestPipEnvironment
* Remove global state and force explicit use of TestPipEnvironment
  instances
* Remove "backup" virtualenv copying and instead create new
  virtual environments each time.
* Remove the monkeypatched "PyPICache" functionality
* Remove things that were not being used anymore and were dead
  weight
* Remove sitecustomize support which was primarily used to
  monkeypatch the "PyPICache" but was used in one or two other
  tests.

* Add a .join() method for a more explicit joining than /
* Return values where possible
* Make glob an iterator
* Remove checks for versions of Python we don't support
* Add a write() function to make it simple to write some text
  into a file
* Add a touch() function to make it simple to ensure a file
  exists

Switch to using py.test as the test runner instead of nose

* Better output with the bare asserts we use throughout the tests
* Function fixtures are pretty nice, especially as a way to
  start a background server or create an isolated virtualenv

Add the universal flag to setup.cfg to create version-independent wheels

tar/zip unpack changes

Warn when using an insecure transport for index or find-links

Minor grammatical fixes in the cookbook