added Source:seek/tell

--HG--
branch : minor

src/modules/audio/null/Source.cpp

@@ -100,6 +100,15 @@ namespace null
 	{
 		return volume;
 	}
+	
+	void Source::seek(float, Source::Unit)
+	{
+	}
+	
+	float Source::tell(Source::Unit) const
+	{
+		return 0.0f;
+	}
 
 	void Source::setPosition(float *)
 	{

src/modules/audio/null/Source.h

@@ -57,6 +57,8 @@ namespace null
 		virtual float getPitch() const;
 		virtual void setVolume(float volume);
 		virtual float getVolume() const;
+		virtual void seek(float offset, Unit unit);
+		virtual float tell(Unit unit) const;
 		virtual void setPosition(float * v);
 		virtual void getPosition(float * v) const;
 		virtual void setVelocity(float * v);