Freeciv

I accidentally tried loading a 2.6 savegame using ruleset 'augmented2' when I didn't have the ruleset available.

This went surprisingly badly:

• The server carried on trying to a few bits of the savegame, such as treaties, even after it was obviously doomed for lack of ruleset. e.g.

  1: Failed to load ruleset
  1: Treaty between unknown players Joyce Banda and Koimala
  ...
  1: In secfile_lookup_str() [/home/jtn/src/freeciv/git26/utility/registry_ini.c:2043]: secfile '/tmp/freeciv-T0089-Y-0275-final.sav.bz2' in section 'NULL': "history.title" entry doesn't exist.
  1: Failure loading savegame!

• The server was left in an unusable state.

  1: in send_ruleset_game() [/home/jtn/src/freeciv/git26/server/ruleset.c::6863]: assertion 'game.veteran != ((void *)0)' failed.

• The client then segfaulted, trying to cope with a NULL game.plr_bg_color/

This patch addresses the server aspects. (For savegame2/3; I'm not touching the legacy pre-2.3 savegame code.)

1. Add a bit more logging, to make it easier to spot the reason for failure to load the ruleset.
2. Most sg_load_*() do a the standard sg_check_ret() at the start of the function, but a few did not. (Hence the random complaints about treaties for nonexistent players.)
3. Change what happens at the end of a failed load attempt: since load_command() does server_game_free() / server_game_init(), do that again, then load a ruleset. (On S2_6, whatever is currently configured; sg_load_ruleset() will have left that sane.) I haven't thoroughly checked this is the right thing to do, but it's closer than what was there before, and seems to work.
   • (I'm not convinced the server implementation of game_reset() is useful for anything. This removes the only call.)