Don't obfuscate the original module name.
Add test case which tests for proper deprecated output based on virtualenv version.
Small code and print's cleanup.
Warn the users if they're using `--distribute` without needing.
Add missing import and instantiate a local logger instance.
Warn and don't pass `--never-download` to `virtualenv` if it's version is `>= 0.10`. Fixes #6030.
Set defaults to `None` instead of `''`.
Allow `extra_search_dir` for `virtualenv.create()` to be passed a list. Fixes #6031.
Add test case to check for proper handling of `--never-download`. Refs #6030.

Also added assertions to check for proper deprecation logging messages output.
Added a test case to check for multiple extra search dirs support. Refs #6031.
Show a deprecation warning if `no_site_packages` is used. Fixes #6027.

If both `no_site_packages` and `system_site_packages` are used, throw an error.
Added the appropriate tests.
Update doc string to make it explicit that it's salt we're mentioning.
`virtualenv` version checking is only done if using `virtualenv` and not `pyvenv`.
Warn about using option not available for `virtualenv` and `pyvenv` respectively.

`False` defaults have been turned into `None` to know if the user is even passing `False` and fail.
Fix the `virtualenv` unittests which rely on it's version changing.
No empty strings as defaults!
Extra care regarding empty strings.
Let us not use a deprecated option ourselves unless for testing the deprecation.
Only `strip()` on strings.
Add test case which tests if non proper arguments raise an exception.