Make HelloWorld plugin always compile, mark as experimental

Task-Nr: QTCREATORBUG-2269

src/plugins/helloworld/HelloWorld.pluginspec

-<plugin name="HelloWorld" version="2.0.90" compatVersion="2.0.90">
+<plugin name="HelloWorld" version="2.0.90" compatVersion="2.0.90" experimental="true">
     <vendor>Nokia Corporation</vendor>
     <copyright>(C) 2010 Nokia Corporation</copyright>
     <license>

src/plugins/helloworld/helloworldplugin.cpp

@@ -30,6 +30,7 @@
 #include "helloworldplugin.h"
 
 #include <coreplugin/actionmanager/actionmanager.h>
+#include <coreplugin/actionmanager/actioncontainer.h>
 #include <coreplugin/basemode.h>
 #include <coreplugin/coreconstants.h>
 #include <coreplugin/icore.h>
@@ -77,9 +78,7 @@ bool HelloWorldPlugin::initialize(const QStringList &arguments, QString *error_m
 
     // Create a unique context id for our own view, that will be used for the
     // menu entry later.
-    QList<int> context = QList<int>()
-        << core->uniqueIDManager()->uniqueIdentifier(
-                QLatin1String("HelloWorld.MainView"));
+    Core::Context context("HelloWorld.MainView");
 
     // Create an action to be triggered by a menu entry
     QAction *helloWorldAction = new QAction(tr("Say \"&Hello World!\""), this);

src/plugins/plugins.pro

@@ -23,7 +23,7 @@ SUBDIRS   = plugin_coreplugin \
             plugin_locator \
             plugin_debugger \
 #            plugin_qtestlib \ # this seems to be dead
-#            plugin_helloworld \ # sample plugin
+            plugin_helloworld \ # sample plugin
             plugin_help \
 #            plugin_regexp \ # don't know what to do with this
             plugin_cpaster \