Cleanup code using forward declarations.

Use misc methods of avoiding unnecesary header includes.
Replace int typedefs with int##_t from stdint.h.
Replace PRI64[xdu] with PRI[xdu]64 from inttypes.h.
Normalize QT_VERSION ifs where possible.
Resolve some indirect dependencies as direct ones.
Remove extern declarations from .cpp files.

src/qt/guiutil.h

@@ -5,19 +5,19 @@
 #ifndef GUIUTIL_H
 #define GUIUTIL_H
 
-#include <QString>
-#include <QObject>
 #include <QMessageBox>
+#include <QObject>
+#include <QString>
 
 class SendCoinsRecipient;
 
 QT_BEGIN_NAMESPACE
+class QAbstractItemView;
+class QDateTime;
 class QFont;
 class QLineEdit;
-class QWidget;
-class QDateTime;
 class QUrl;
-class QAbstractItemView;
+class QWidget;
 QT_END_NAMESPACE
 
 /** Utility functions used by the Bitcoin Qt UI.