`any?` is not the opposite of `empty?`. Besides the case that
`[false, nil].any?` will return false, `any?`(O(n)) has much worse
performance than `empty?`(O(1)).

* python: tweak script linking in virtualenv

Instead of making the formula author use a slightly awkward block like

  venv.link_scripts(bin) { venv.pip_install buildpath }

avoid exposing this implementation detail and offer the more familiar:

  venv.pip_install buildpath, :link_scripts => bin

* Add non-block form and use instead of recursion

* Update 'pip_install' documentation

* Remove obsolete 'link_scripts'

* Add test for 'pip_install' with linking scripts

Also drop no longer relevant (and broken) `link_scripts` test, that
served as a template for the new test.

* Restore compatibility with Ruby 1.8.7

* Replace option hash with 'pip_install_and_link'

* Avoid confusing 'Object#tap' and fix silly bug

* Avoid side effects in mock object parameter check

* Simplify argument check (no need for a block)

Allow virtualenvs to find Python bindings provided by deps

Closes #603.

Instead of adding additional lines to formula.rb:
  https://git.io/vKxxh
just turn on argument refurbishment for any formula that creates a
virtualenv.

cf Homebrew/ruby-macho#50, Homebrew/homebrew-core#1663