add a --fakechain argument for tests

The core tests use the blockchain, and reset it to be able
to add test data to it. This does not play nice with the
databases, since those will save that data without an explicit
save call.
We add a fakechain flag that the tests will set, which tells
the core and blockchain code to use a separate database, as
well as skip a few things like checkpoints and fixup, which
only make sense for real data.

tests/core_tests/chaingen.h

@@ -484,6 +484,10 @@ inline bool do_replay_events(std::vector<test_event_entry>& events)
   if (!r)
     return false;
 
+  // hardcode a --fakechain option for tests
+  static const char * const fakechain[] = {"", "--fakechain"};
+  boost::program_options::store(boost::program_options::parse_command_line(2, fakechain, desc), vm);
+
   cryptonote::cryptonote_protocol_stub pr; //TODO: stub only for this kind of test, make real validation of relayed objects
   cryptonote::core c(&pr);
   // FIXME: make sure that vm has arg_testnet_on set to true or false if