(windows) Swapping out cmd.exe example

This now displays something that would run and exit with proper exit code
(windows) Allow Puppet version to be specified

This allows you to specify the version you want and the url is updated
accordingly. Also updated the MSI to the latest stable release.
(windows) MSI install from url

MSIs can be installed from a URL so there is not a need to download it
separately. This also switches the order of arguments passed to msiexec to be
more appropriate.

This also allows the MSI location to be local or on a share since it won't
attempt to download it first.
(windows) Do not install puppet if already installed

If the puppet command exists, do not attempt to reinstall puppet. Note that
this will only work if puppet is put on the PATH. This is done automatically
starting with Puppet 3.3.1 MSI (
http://docs.puppetlabs.com/windows/installing.html#after-installation ).
Merge pull request #18 from ferventcoder/maint/master/simplify_windows

Windows.ps1 Cleanup