core_tests: add tests for hard fork behaviors (MRL-0004)

We also replace the --fakechain option with an optional structure
containing details about configuration for the core/blockchain,
for test purposes. This seems more future friendly.

src/common/command_line.h

@@ -215,5 +215,4 @@ namespace command_line
   extern const arg_descriptor<uint64_t> arg_prep_blocks_threads;
   extern const arg_descriptor<uint64_t> arg_db_auto_remove_logs;
   extern const arg_descriptor<uint64_t> arg_show_time_stats;
-  extern const arg_descriptor<bool> arg_fakechain;
 }