title: Add function to output error string on Google Test assertions
body: <p>I would like to have a function I can stream to an <code>ASSERT_</code>.  Something I could use like this:</p>
  
  <pre><code>ASSERT_EQ(std::remove(someFile), 0) &lt;&lt; displayErrStr(__LINE__);
  </code></pre>
  
  <p>And the output would be</p>
  
  <pre><code>test.cc:32: Failure
        Expected: std::remove(someFile)
        Which is: -1
  To be equal to: 0
  Error at line 32: Directory not empty
  </code></pre>
  
  <p>I can do it by adding <code>&lt;&lt; "Error at line " &lt;&lt; __LINE__ &lt;&lt; ": " &lt;&lt; strerror(errno)</code> to every relevant line but this is more verbose than I want.</p>
  
  <p>I assume this is possible but I'm not a C++ expert.</p>