Show more useful error dialog in case of plugin errors.

Task-number: QTCREATORBUG-3940

Change-Id: I9e12ad68bba9c2f0d8f5243ab7dc763765fba756
Reviewed-on: http://codereview.qt.nokia.com/3811
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@nokia.com>

src/libs/extensionsystem/pluginmanager.cpp

@@ -328,6 +328,22 @@ void PluginManager::loadPlugins()
     return d->loadPlugins();
 }
 
+/*!
+    \fn bool PluginManager::hasError() const
+    Returns true if any plugin has errors even though it is enabled.
+    Most useful to call after loadPlugins().
+*/
+bool PluginManager::hasError() const
+{
+    foreach (PluginSpec *spec, plugins()) {
+        // only show errors on startup if plugin is enabled.
+        if (spec->hasError() && spec->isEnabled() && !spec->isDisabledIndirectly()) {
+            return true;
+        }
+    }
+    return false;
+}
+
 /*!
     \fn void PluginManager::shutdown()
     Shuts down and deletes all plugins.