title: MEF composition issue
body: <p>I can't solve what seems to be a basic MEF problem:
  I have 2 "plugins" project (which we'll call P1 and P2), and a third project that is common to both plugins (which we'll call C). P1 and P2 both reference C.</p>
  
  <p>When trying to import a component that lives in P1, it fails because this component has dependencies on components that live in C.</p>
  
  <p>Here is the trace:</p>
  
  <blockquote>
    <p>System.ComponentModel.Composition Warning: 1 : The ComposablePartDefinition 'MyCompany.Client.Pms.Plugin.InclusionList.ViewModel.InclusionListViewModel' has been rejected. The composition remains unchanged. The changes were rejected because of the following error(s): The composition produced multiple composition errors, with 4 root causes. The root causes are provided below. Review the CompositionException.Errors property for more detailed information.</p>
    
    <p>1) <strong>No exports were found that match the constraint</strong> '((exportDefinition.ContractName = "MyCompany.Client.Plugins.Common.Controls.Selectors.PortfolioSelectors.ViewModel.ICalypsoBookSelectorViewModel") &amp;&amp; (exportDefinition.Metadata.ContainsKey("ExportTypeIdentity") &amp;&amp; "MyCompany.Client.Plugins.Common.Controls.Selectors.PortfolioSelectors.ViewModel.ICalypsoBookSelectorViewModel".Equals(exportDefinition.Metadata.get_Item("ExportTypeIdentity"))))'.</p>
    
    <p>Resulting in: Cannot set import 'MyCompany.Client.Pms.Plugin.InclusionList.ViewModel.InclusionListViewModel.CalypsoBookSelectorViewModel (ContractName="MyCompany.Client.Plugins.Common.Controls.Selectors.PortfolioSelectors.ViewModel.ICalypsoBookSelectorViewModel")' on part 'MyCompany.Client.Pms.Plugin.InclusionList.ViewModel.InclusionListViewModel'.
    Element: MyCompany.Client.Pms.Plugin.InclusionList.ViewModel.InclusionListViewModel.CalypsoBookSelectorViewModel (ContractName="MyCompany.Client.Plugins.Common.Controls.Selectors.PortfolioSelectors.ViewModel.ICalypsoBookSelectorViewModel") -->  MyCompany.Client.Pms.Plugin.InclusionList.ViewModel.InclusionListViewModel -->  DirectoryCatalog (Path="C:\Work\mmtrader\dashboard\Code\Src\Dashboard\MM\Trader\bin\Debug\Plugins\Positions")</p>
  </blockquote>
  
  <p>[...] (The 3 other problems are exactly the same, on different view models)</p>
  
  <p>I have looked at the MEF catalog, and it turns out that MEF knows about those view models, so I don't know what's missing.</p>
  
  <p>As requested by Dennis below, here are my import/export:</p>
  
  <p>Export:</p>
  
  <pre><code>Export(typeof(ICalypsoBookSelectorViewModel))]
  public class CalypsoBookSelectorViewModel : ScreenWithCleanupLifecycle, ICalypsoBookSelectorViewModel
  {...}
  </code></pre>
  
  <p>Import:</p>
  
  <pre><code>[Import(typeof(ICalypsoBookSelectorViewModel))]
  public ICalypsoBookSelectorViewModel CalypsoBookSelectorViewModel { get; set; }
  </code></pre>
  
  <p>And the catalog:</p>
  
  <p><img src="https://i.stack.imgur.com/mU19K.png" alt="Catalog"></p>
  
  <p>Thanks in advance for your help!</p>