title: waitForExpectationsWithTimeout crashes
body: <p>I am trying to test an asynchronous request with XCTest and so using expectationWithDescription:.
  Yet when waitForExpectationsWithTimeout is called it immediately crashes without even waiting for the timeout.
  I even tried putting the fulfill operation soon after just to exclude a timeout issue, but it di no change things; this is my function:</p>
  
  <pre><code>func testTrafficRefresh(){
      let expectation = expectationWithDescription("refreshed")
      waitForExpectationsWithTimeout(10, handler:nil)
      traffic.trafficRefresh {[weak self] () -&gt; Void in
          let coming=inArrivoHDDetailViewController.sharedDetailController().activeTransit
          let buses=self!.traffic.arrivingBuses
          let count=buses.count
          XCTAssert(count==0 &amp;&amp; coming==0, "No buses and active transit")
          XCTAssert(count&gt;0 &amp;&amp; coming==1, "Arriving buses and inactive transit")
          expectation.fulfill()   
      }
  }
  </code></pre>
  
  <p>The same behavior happens in other functions. If I take away the waitForExpectationsWithTimeout operation and keep the expectationWithDescription operation, it crashes at the end of the function. In both case the crash repot is the following:</p>
  
  <blockquote>
  <pre><code>libsystem_kernel.dylib`__pthread_kill:
  0x10723227c &lt;+0&gt;:  movl   $0x2000148, %eax
  0x107232281 &lt;+5&gt;:  movq   %rcx, %r10
  0x107232284 &lt;+8&gt;:  syscall 
  0x107232286 &lt;+10&gt;: jae    0x107232290               ; &lt;+20&gt;
  0x107232288 &lt;+12&gt;: movq   %rax, %rdi
  0x10723228b &lt;+15&gt;: jmp    0x10722dc53               ; cerror_nocancel
  0x107232290 &lt;+20&gt;: retq   
  0x107232291 &lt;+21&gt;: nop    
  0x107232292 &lt;+22&gt;: nop    
  0x107232293 &lt;+23&gt;: nop
  </code></pre>
  </blockquote>