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/sendcoinsdialog.h

@@ -8,12 +8,8 @@
 #include "walletmodel.h"
 
 #include <QDialog>
-#include <QVariant>
-#include <QPair>
 
-namespace Ui {
-    class SendCoinsDialog;
-}
+class OptionsModel;
 class SendCoinsEntry;
 class SendCoinsRecipient;
 
@@ -21,6 +17,10 @@ QT_BEGIN_NAMESPACE
 class QUrl;
 QT_END_NAMESPACE
 
+namespace Ui {
+    class SendCoinsDialog;
+}
+
 /** Dialog for sending bitcoins */
 class SendCoinsDialog : public QDialog
 {