fix: don't crash/terminate upon errors within chokidar

Handle errors from chokidar and route them to the console. Previously,
these unhandled errors (which are very common when editing in Visual
Studio) would cause karma to terminate and all browsers to vanish. Fixes
#959

lib/watcher.js

@@ -94,7 +94,12 @@ exports.watch = function(patterns, excludes, fileList, usePolling) {
   // register events
   chokidarWatcher.on('add', bind(fileList.addFile))
                  .on('change', bind(fileList.changeFile))
-                 .on('unlink', bind(fileList.removeFile));
+                 .on('unlink', bind(fileList.removeFile))
+                 // If we don't subscribe; unhandled errors from Chokidar will bring Karma down
+                 // (see GH Issue #959)
+                 .on('error', function(e) {
+                    log.debug(e);
+                  });
 
   return chokidarWatcher;
 };