Mercurial: Compile windows, use common output window.

Polish: Canconical slots, const-correctness, some QLatin1Strings/tr,

src/plugins/mercurial/mercurialclient.h

@@ -31,10 +31,12 @@
 #define MERCURIALCLIENT_H
 
 #include <QtCore/QObject>
-#include <QtCore/QFileInfo>
-#include <QtCore/QByteArray>
 #include <QtCore/QPair>
 
+QT_BEGIN_NAMESPACE
+class QFileInfo;
+QT_END_NAMESPACE
+
 namespace Core {
 class ICore;
 }