VCS: Do not try to add files that are already tracked

Task-number: QTCREATORBUG-2455
Change-Id: I4b1fa9676ad4a8d7293e035e4d6103251bef8aee
Reviewed-by: Nikita Baryshnikov <nib952051@gmail.com>
Reviewed-by: Cristian Tibirna <tibirna@kde.org>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/bazaar/bazaarclient.h

@@ -57,6 +57,7 @@ public:
     void view(const QString &source, const QString &id,
               const QStringList &extraOptions = QStringList());
     QString findTopLevelForFile(const QFileInfo &file) const;
+    bool managesFile(const QString &workingDirectory, const QString &fileName) const;
 
 protected:
     Core::Id vcsEditorKind(VcsCommand cmd) const;