feat(client): show error if no adapter is included

Before this fix, Karma would just execute "an empty" test suite. The next run would however end up with an exception (Property "start" is not a function).

This should make it easier to understand.

Author: vojtajina

client/karma.js

@@ -177,7 +177,9 @@ var Karma = function(socket, context, navigator, location) {
 
   // supposed to be overriden by the context
   // TODO(vojta): support multiple callbacks (queue)
-  this.start = this.complete;
+  this.start = function() {
+    this.error('You need to include some adapter that implements __karma__.start method!');
+  };
 
   socket.on('execute', function(cfg) {
     // reset hasError and reload the iframe