Replace several network protocol version numbers with named constants

stored in version.h.

Also, a minor CAddress code reformat while we're in there, fixing
some incorrect indentation.

src/protocol.h

@@ -79,9 +79,10 @@ class CAddress : public CService
              if (fRead)
                  pthis->Init();
              if (nType & SER_DISK)
-             READWRITE(nVersion);
-             if ((nType & SER_DISK) || (nVersion >= 31402 && !(nType & SER_GETHASH)))
-             READWRITE(nTime);
+                 READWRITE(nVersion);
+             if ((nType & SER_DISK) ||
+                 (nVersion >= CADDR_TIME_VERSION && !(nType & SER_GETHASH)))
+                 READWRITE(nTime);
              READWRITE(nServices);
              READWRITE(*pip);
             )