Refs #482: fixed a regression in clitests

One test of clitests loads about:blank. However, there
is no navigationRequested event and so our new browserInitializing
flag is not toggled to false, and then checkStep() is blocking
tests. Let's toggle it inside onLoadStarted too.

@@ -2366,6 +2366,9 @@ function createPage(casper) {
         }
     };
     page.onLoadStarted = function onLoadStarted() {
+        // in some case, there is no navigation requested event, so
+        // be sure that browserInitializing is false to not block checkStep()
+        casper.browserInitializing = false;
         casper.loadInProgress = true;
         casper.emit('load.started');
     };