title: Import external definitions
body: <p>With Typescript, is there a way to import just the types from an external module?</p>
  
  <p>Basically I just want one module to know the typings from another (to power Intellisense), but without the import being emitted in JavaScript. I want to do this because the module in question may or may not have been loaded - i.e. there isn't a hard dependency, but I want to have some typed code that runs and uses the module if it is there.</p>
  
  <p>Hope this is clear.</p>