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/macnotificationhandler.h

@@ -4,6 +4,7 @@
 
 #ifndef MACNOTIFICATIONHANDLER_H
 #define MACNOTIFICATIONHANDLER_H
+
 #include <QObject>
 
 /** Macintosh-specific notification handler (supports UserNotificationCenter and Growl).