Don't allow opening the same generic project multiple times

Quick fix by copying code also found in Qt4 and QML project managers.
Would be better to have some common solution...

Task-number: QTCREATORBUG-1383

src/plugins/genericprojectmanager/genericprojectmanager.cpp

@@ -32,8 +32,11 @@
 #include "genericproject.h"
 
 #include <coreplugin/icore.h>
+#include <coreplugin/messagemanager.h>
 #include <coreplugin/uniqueidmanager.h>
+#include <projectexplorer/projectexplorer.h>
 #include <projectexplorer/projectexplorerconstants.h>
+#include <projectexplorer/session.h>
 
 #include <QtDebug>
 
@@ -60,14 +63,21 @@ QString Manager::mimeType() const
 
 ProjectExplorer::Project *Manager::openProject(const QString &fileName)
 {
-    QFileInfo fileInfo(fileName);
+    if (!QFileInfo(fileName).isFile())
+        return 0;
 
-    if (fileInfo.isFile()) {
-        GenericProject *project = new GenericProject(this, fileName);
-        return project;
+    ProjectExplorer::ProjectExplorerPlugin *projectExplorer = ProjectExplorer::ProjectExplorerPlugin::instance();
+    foreach (ProjectExplorer::Project *pi, projectExplorer->session()->projects()) {
+        if (fileName == pi->file()->fileName()) {
+            Core::MessageManager *messageManager = Core::ICore::instance()->messageManager();
+            messageManager->printToOutputPanePopup(tr("Failed opening project '%1': Project already open")
+                                                   .arg(QDir::toNativeSeparators(fileName)));
+            return 0;
+        }
     }
 
-    return 0;
+    GenericProject *project = new GenericProject(this, fileName);
+    return project;
 }
 
 void Manager::registerProject(GenericProject *project)

src/plugins/genericprojectmanager/genericprojectmanager.h

@@ -37,7 +37,7 @@ namespace Internal {
 
 class GenericProject;
 
-class Manager: public ProjectExplorer::IProjectManager
+class Manager : public ProjectExplorer::IProjectManager
 {
     Q_OBJECT
 

src/plugins/qt4projectmanager/qt4projectmanager.cpp

@@ -181,7 +181,7 @@ QString Qt4Manager::mimeType() const
     return QLatin1String(Qt4ProjectManager::Constants::PROFILE_MIMETYPE);
 }
 
-ProjectExplorer::Project* Qt4Manager::openProject(const QString &fileName)
+ProjectExplorer::Project *Qt4Manager::openProject(const QString &fileName)
 {
     Core::MessageManager *messageManager = Core::ICore::instance()->messageManager();
 

src/plugins/qt4projectmanager/qt4projectmanager.h

@@ -79,7 +79,7 @@ public:
     int projectLanguage() const;
 
     virtual QString mimeType() const;
-    ProjectExplorer::Project* openProject(const QString &fileName);
+    ProjectExplorer::Project *openProject(const QString &fileName);
 
     // Context information used in the slot implementations
     ProjectExplorer::Node *contextNode() const;