Breath cheat fix: server side

Breath is now handled server side. Changing this behaviour required some modifications to core:

* Ignore TOSERVER_BREATH package, marking it as obsolete
* Clients doesn't send the breath to server anymore
* Use PlayerSAO pointer instead of peer_id in Server::SendPlayerBreath to prevent a useless lookup (little perf gain)
* drop a useless static_cast in emergePlayer

src/content_sao.h

@@ -20,6 +20,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #ifndef CONTENT_SAO_HEADER
 #define CONTENT_SAO_HEADER
 
+#include <util/numeric.h>
 #include "serverobject.h"
 #include "itemgroup.h"
 #include "object_properties.h"
@@ -232,7 +233,7 @@ public:
 	void setHPRaw(s16 hp) { m_hp = hp; }
 	s16 readDamage();
 	u16 getBreath() const { return m_breath; }
-	void setBreath(const u16 breath);
+	void setBreath(const u16 breath, bool send = true);
 	void setArmorGroups(const ItemGroupList &armor_groups);
 	ItemGroupList getArmorGroups();
 	void setAnimation(v2f frame_range, float frame_speed, float frame_blend, bool frame_loop);
@@ -339,6 +340,10 @@ private:
 	v3s16 m_nocheat_dig_pos;
 	float m_nocheat_dig_time;
 
+	// Timers
+	IntervalLimiter m_breathing_interval;
+	IntervalLimiter m_drowning_interval;
+
 	int m_wield_index;
 	bool m_position_not_sent;
 	ItemGroupList m_armor_groups;