title: Rollup.js how import a js file (not es6 module) without any change (myvar$extrastring)
body: <p>First of all, i understand why rollup.js need to append extra string at the end of certain variable to avoid collision but... 
  I don't understand how to "concat/import" a simple javascript file who is not an amd/commonjs/es6, but simple revealing module !</p>
  
  <p>I have the following file structure:</p>
  
  <p>foo.js</p>
  
  <pre><code>var Foo = (function () {
  
      var someMethod = function () {};
  
      return {
          someMethod: someMethod
      };
  
  })();
  </code></pre>
  
  <p>bar.js</p>
  
  <pre><code>(function(module) {
  
      module.bar = "bar";
  
  })(Foo);
  </code></pre>
  
  <p>main.js</p>
  
  <pre><code>import "foo.js"
  import "bar.js"
  </code></pre>
  
  <p>after building, i got:</p>
  
  <p>build.js</p>
  
  <pre><code>var Foo$1 = (function () { // Here the problem
  
      var someMethod = function () {};
  
      return {
          someMethod: someMethod
      };
  
  })();
  
  (function(module) {
  
      module.bar = "bar";
  
  })(Foo); // Ouupss !
  </code></pre>
  
  <p>So how can i got Foo instead of Foo$1 ? Or Foo$1 instead of Foo for bar.js ?</p>
  
  <p>Edit: </p>
  
  <p>In case, where in main.js, i use default import in view to override the default name:</p>
  
  <pre><code>import Foo from "foo.js"
  </code></pre>
  
  <p>i got an error like this (normal !):</p>
  
  <blockquote>
    <p>Non-existent export 'default' is imported from foo.js by main.js</p>
  </blockquote>
  
  <p>It's a misunderstanding, but after research on stackoverflow and internet i found nothing about how can i resolve this tricky problem. </p>
  
  <p>So... thanks in advance !</p>