Prevented project's existing .pro file from being added to project

A project's existing .pro file could be added to the project, making
the .pro file appear twice in the project tree. This is sub-optimal
because

1. It does not make sense for the .pro file to appear twice.
2. Qt Creator crashes when trying to remove either of the duplicate
.pro files.

src/plugins/qt4projectmanager/qt4nodes.cpp

@@ -391,7 +391,10 @@ void Qt4PriFileNode::changeFiles(const FileType fileType,
         }
         const QModelIndex varIndex = root.child(row, 0);
 
+        const QString &proFilePath = includeFile->fileName();
         foreach (const QString &filePath, filePaths) {
+            if (filePath == proFilePath)
+                continue;
             const QString &relativeFilePath = priFileDir.relativeFilePath(filePath);
             proModel.insertItem(new ProValue(relativeFilePath, proVar),
                                 proModel.rowCount(varIndex), varIndex);