Add --no-setuptools and --no-pip options.

In specialised circumstances (e.g., when testing new versions of distribute
or pip) it can be useful to create a virtualenv which does not include these
packages pre-installed. Add options to specify that when creating the
virtualenv.
pythonX.Y symlinks should be made on all platforms

The comment on line 1412 ("Some tools depend on pythonX.Y being
present") is accurate on all platforms, but the block of code that
ensures that pythonX.Y is present is inside a conditional that checks
"if '.framework' in prefix".

This commit moves the code out of the conditional so that it applies on
all platforms.
Ensure all permutations of version name exist

This ensures that all required names are symlinked to py_executable.
Note that it does not do this on windows, as I am not sure what the
requirements are there (pythonX.Y.exe?), and it didn't do this
previously anyway.

This will fix #347 as well as #341.
Refactoring to show logic better
Merge pull request #354 from piotr-dobrogost/activate_deactivate_refactoring

Refactoring to show logic better
Add a --setuptools option (which implicitly adds $VIRTUALENV_SETUPTOOLS)
envar, for overriding any default use of distribute.  No-op in Python 3.
Explicitly set use_distribute to False, which makes it easier to change to
True in Debian.
Create symlinks in bin_dir, not cwd
Test that symlinks are properly created in bin_dir
Fix typos in test names
Merge pull request #341 from vhata/pythonX.Y

pythonX.Y symlinks should be made on all platforms
Updated embedded scripts.
Merge pull request #356 from warsaw/setuptools

Add a --setuptools option
Merge branch 'develop' of github.com:pypa/virtualenv into develop
Updated changelog.
Bumped version up a notch.
Merge branch 'release/1.8.3' into develop
All setup.py-style cli arguments are conditional on egg_path.

Refactor the cli-building a bit to remove a few levels of nesting.

Closes #358.
Add an integration test for the download case.
Measure test coverage.