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/git/gitversioncontrol.h

@@ -51,6 +51,7 @@ public:
 
     bool managesDirectory(const QString &directory, QString *topLevel) const;
 
+    bool isConfigured() const;
     bool supportsOperation(Operation operation) const;
     bool vcsOpen(const QString &fileName);
     bool vcsAdd(const QString &fileName);
@@ -70,7 +71,6 @@ public:
     void emitRepositoryChanged(const QString &);
 
 private:
-    bool m_enabled;
     GitClient *m_client;
 };