Fix #109: Bug in calculation of milirary score
popup: Fix calculation of convertible knights, which would otherwise result in random sprites being drawn
Fix bugs in lists of defending serfs

game: In update_building_castle() increment castle_knights when promoting serf to knight. Also, clear inventory pointer to avoid promoting the same serf twice.
popup, serf: Fix iteration and prepending to knight list.
game: Define max number of players as GAME_MAX_PLAYER_COUNT

Fix #111: Off-by-one error in calculating knight morale
flag: Fix bug caused by missing check in flag_prioritize_pickup()
Fix #114: Allow knight in state OCCUPY ENEMY BUILDING to enter own castle

This situation should not really happen, since an enemy castle cannot be occupied (only demolished). But this fix adds the missing case anyway because it might be needed later, and because it allows the game to gracefully recover from other bugs that may cause this situation.
Fix #115: Fix gaps in drawing of statistics chart
Fix #112: serf FREE WALKING direction badly calculated when offset is negative
Bump version to 0.1-rc3
Merge bug fixes from v0.1-rc3