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/mruset.h

@@ -1,11 +1,13 @@
 // 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 BITCOIN_MRUSET_H
 #define BITCOIN_MRUSET_H
 
-#include <set>
 #include <deque>
+#include <set>
+#include <utility>
 
 /** STL-like set container that only keeps the most recent N elements. */
 template <typename T> class mruset