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/checkqueue.h

@@ -1,16 +1,17 @@
 // Copyright (c) 2012 The Bitcoin developers
 // Distributed under the MIT/X11 software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
 #ifndef CHECKQUEUE_H
 #define CHECKQUEUE_H
 
-#include <boost/foreach.hpp>
-#include <boost/thread/mutex.hpp>
-#include <boost/thread/locks.hpp>
-#include <boost/thread/condition_variable.hpp>
-
-#include <vector>
 #include <algorithm>
+#include <vector>
+
+#include <boost/foreach.hpp>
+#include <boost/thread/condition_variable.hpp>
+#include <boost/thread/locks.hpp>
+#include <boost/thread/mutex.hpp>
 
 template<typename T> class CCheckQueueControl;