VCS: Do not claim to support any operation if unconfigured

Make sure none of the VCS systems claims it does support any
VCS operation while unconfigured. This stops the specific
VCS from showing up in wizards, etc. till they can actually
be used.

src/plugins/coreplugin/iversioncontrol.h

@@ -75,8 +75,14 @@ public:
 
     virtual bool managesDirectory(const QString &filename, QString *topLevel = 0) const = 0;
 
+    /*!
+     * Returns true is the VCS is configured to run.
+     */
+    virtual bool isConfigured() const = 0;
     /*!
      * Called to query whether a VCS supports the respective operations.
+     *
+     * Return false if the VCS is not configured yet.
      */
     virtual bool supportsOperation(Operation operation) const = 0;