title: Reuse NUnit's IConstraint in validation
body: <p>NUnit has an IConstraint interface (<a href="http://www.nunit.org/index.php?p=constraintModel&amp;r=2.4" rel="nofollow">documentation here</a> and <a href="https://github.com/nunit/nunit-framework/blob/5d9a9b2d3ae49892b60f31849d698865d17cbad0/src/framework/Constraints/IConstraint.cs" rel="nofollow">code here</a>). It seems to me that reusing this type in my core project for validation purposes makes sense.</p>
  
  <p>Are there unforseen side effects I have not yet recognized? Would you reuse the IConstraint type in your core project? why/why not?</p>