title: wix generating new upgrade code
body: <p>My project needs to have the ability to install 2 versions or more simultaneously.
  as far as i can find, the solution i have found is changing the upgrade code for each build of the installer.</p>
  
  <p>however i want to do this automatically. in regular GUID i just use "*" but this won't work for upgradecode.
  is there a way to generate new upgradecode in every wix prebuild or any other solution? </p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;Wix xmlns="http://schemas.microsoft.com/wix/2006/wi" xmlns:util="http://schemas.microsoft.com/wix/UtilExtension" xmlns:bal="http://schemas.microsoft.com/wix/BalExtension" xmlns:netfx="http://schemas.microsoft.com/wix/NetFxExtension"&gt;
    &lt;Bundle Name="Prog" Version="1.2.1.16" Manufacturer="Gilad Corporation" UpgradeCode="{7E71F945-BA46-4872-A6B2-AF992FFDF2D0}"&gt;
      &lt;BootstrapperApplicationRef Id="WixStandardBootstrapperApplication.RtfLicense"&gt;
        &lt;bal:WixStandardBootstrapperApplication LicenseFile="..\SetupProject\Gilad.rtf" /&gt;
      &lt;/BootstrapperApplicationRef&gt;
      &lt;Chain&gt;
        &lt;!-- TODO: Define the list of chained packages. --&gt;
        &lt;PackageGroupRef Id="Netfx45FullPackage" /&gt;
      &lt;/Chain&gt;
    &lt;/Bundle&gt;
  </code></pre>