Revert "Delete old protocol version constants and simplify code that used them."

This reverts commit 5a49c929dd.

src/protocol.h

@@ -103,7 +103,8 @@ public:
             Init();
         if (nType & SER_DISK)
             READWRITE(nVersion);
-        if ((nType & SER_DISK) || !(nType & SER_GETHASH))
+        if ((nType & SER_DISK) ||
+            (nVersion >= CADDR_TIME_VERSION && !(nType & SER_GETHASH)))
             READWRITE(nTime);
         READWRITE(nServices);
         READWRITE(*(CService*)this);