title: @try/@catch doesn't catch exception
body: <p>After upgrading Xcode from 6.0 to 6.3, I noticed my automated tests started failing.</p>
  
  <pre><code>2015-04-14 18:56:50.625 xctest[48304:517820] *** Terminating app due to uncaught exception 'foo', reason: 'bar'
  *** First throw call stack:
  (
      0   CoreFoundation                      0x0084a746 __exceptionPreprocess + 182
      1   libobjc.A.dylib                     0x004d3a97 objc_exception_throw + 44
      2   CoreFoundation                      0x0084a66d +[NSException raise:format:] + 141
      3   TestTests                           0x03e6dbdc -[TestTest test] + 810
      4   CoreFoundation                      0x0072b84d __invoking___ + 29
      5   CoreFoundation                      0x0072b6f8 -[NSInvocation invoke] + 360
      6   XCTest                              0x20108975 -[XCTestCase invokeTest] + 320
      7   XCTest                              0x20108baa -[XCTestCase performTest:] + 175
      8   XCTest                              0x20114122 -[XCTest run] + 314
      9   XCTest                              0x20107598 -[XCTestSuite performTest:] + 406
      10  XCTest                              0x20114122 -[XCTest run] + 314
      11  XCTest                              0x20107598 -[XCTestSuite performTest:] + 406
      12  XCTest                              0x20114122 -[XCTest run] + 314
      13  XCTest                              0x20107598 -[XCTestSuite performTest:] + 406
      14  XCTest                              0x20114122 -[XCTest run] + 314
      15  XCTest                              0x20103df2 __25-[XCTestDriver _runSuite]_block_invoke + 61
      16  XCTest                              0x20110c42 -[XCTestObservationCenter _observeTestExecutionForBlock:] + 184
      17  XCTest                              0x20103d16 -[XCTestDriver _runSuite] + 285
      18  XCTest                              0x20104961 -[XCTestDriver _checkForTestManager] + 272
      19  XCTest                              0x20104c79 -[XCTestDriver runTestSuite:completionHandler:] + 376
      20  XCTest                              0x2011772c +[XCTestProbe runTests:] + 216
      21  libobjc.A.dylib                     0x004e967e +[NSObject performSelector:withObject:] + 70
      22  xctest                              0x0000823a xctest + 4666
      23  xctest                              0x000084b0 xctest + 5296
      24  xctest                              0x00008591 xctest + 5521
      25  xctest                              0x00007e3d xctest + 3645
      26  libdyld.dylib                       0x019d4ac9 start + 1
  )
  libc++abi.dylib: terminating with uncaught exception of type NSException
  </code></pre>
  
  <p>After further investigation it appears exceptions are now uncatchable. Both these snippets would cause this error.</p>
  
  <pre><code>XCTAssertThrows([NSException raise:@"foo" format:@"bar"]);
  </code></pre>
  
  <p>and </p>
  
  <pre><code>@try {
      [NSException raise:@"foo" format:@"bar"];
  }
  @catch (NSException *ex) {
      NSLog(@"caught");
  }
  </code></pre>
  
  <p>After a VCS force clean sync and rebuild everything looked fine, but then the same failure started in a couple of builds time. Does anyone have any ideas?</p>