title: add msbuild property in nuget
body: <p>I want to create a nuget package that will add a custom msbuild property before PostBuildEvent property (because I need to use it inside post build event) and after imports (so that I can use TargetDir property) without the user being asked to reload the solution. Is this possible?</p>
  
  <p>I tried using Set-MSBuildProperty from NuGet Power Tools, but that adds property in first property group; I also tried Get-MSBuildProject and "$buildProject.Xml.AddPropertyGroup().AddProperty()", but that adds new property group after immediately after last existing property group (but that may still be before imports). What's worse, both these methods result in an ugly dialog that asks whether changes to project files should be discarded or overwritten (both terms sound equally bad).</p>