Mercurial: Emit version control changed() signals correctly.

Add a QVariant cookie to HgTask to be emitted on successful
execution, wired to IVersionControl.

src/plugins/mercurial/mercurialcontrol.h

@@ -32,6 +32,10 @@
 
 #include <coreplugin/iversioncontrol.h>
 
+QT_BEGIN_NAMESPACE
+class QVariant;
+QT_END_NAMESPACE
+
 namespace Mercurial {
 namespace Internal {
 
@@ -56,6 +60,12 @@ public:
     bool vcsDelete(const QString &filename);
     bool sccManaged(const QString &filename);
 
+public slots:
+    // To be connected to the HgTask's success signal to emit the repository/
+    // files changed signals according to the variant's type:
+    // String -> repository, StringList -> files
+    void changed(const QVariant&);
+
 signals:
     void enabledChanged(bool);