Move network-time related functions to timedata.cpp/h

The network time-offset-mangement functions from util.cpp are moved to
timedata.(cpp|h). This breaks the dependency of util on netbase.

src/timedata.h

@@ -0,0 +1,17 @@
+// Copyright (c) 2014 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_TIMEDATA_H
+#define BITCOIN_TIMEDATA_H
+
+#include <stdint.h>
+
+class CNetAddr;
+
+/* Functions to keep track of adjusted P2P time */
+int64_t GetTimeOffset();
+int64_t GetAdjustedTime();
+void AddTimeData(const CNetAddr& ip, int64_t nTime);
+
+#endif