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/test/key_tests.cpp

@@ -1,12 +1,14 @@
-#include <boost/test/unit_test.hpp>
+#include "key.h"
+
+#include "base58.h"
+#include "script.h"
+#include "uint256.h"
+#include "util.h"
 
 #include <string>
 #include <vector>
 
-#include "key.h"
-#include "base58.h"
-#include "uint256.h"
-#include "util.h"
+#include <boost/test/unit_test.hpp>
 
 using namespace std;