message: Add TheSeven's dnsseed
  TheSeven has kindly provided an auto dns seed service for peercoin. This change adds TheSeven's dnsseed to the dnsseed list.(cherry picked from commit 6e09a5f6d36b229dcd1f4ca04ea899d97775360e)
diff: @@ -1199,6 +1199,7 @@ void MapPort(bool)
  static const char *strMainNetDNSSeed[][2] = {
  {"seed", "seed.ppcoin.net"},
  {"seedppc", "seedppc.ppcoin.net"},
  + {"7server", "ppcseed.ns.7server.net"},
  {"altcointech", "dnsseed.ppc.altcointech.net"},
  {"diandianbi", "seed.diandianbi.org"},
  {NULL, NULL}
  