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/version.cpp

@@ -1,10 +1,11 @@
 // 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.
-#include <string>
 
 #include "version.h"
 
+#include <string>
+
 // Name of client reported in the 'version' message. Report the same name
 // for both bitcoind and bitcoin-qt, to make it harder for attackers to
 // target servers or GUI users specifically.