db/{simple,proxy}, ...: add "override" keywords

Fixes -Winconsistent-missing-override (clang 3.6).

src/db/ProxyDatabasePlugin.cxx

@@ -57,7 +57,7 @@ public:
 	virtual void Close() override;
 	virtual Song *GetSong(const char *uri_utf8,
 				     Error &error) const override;
-	virtual void ReturnSong(Song *song) const;
+	void ReturnSong(Song *song) const override;
 
 	virtual bool Visit(const DatabaseSelection &selection,
 			   VisitDirectory visit_directory,

src/db/SimpleDatabasePlugin.hxx

@@ -61,7 +61,7 @@ public:
 
 	virtual Song *GetSong(const char *uri_utf8,
 			      Error &error) const override;
-	virtual void ReturnSong(Song *song) const;
+	void ReturnSong(Song *song) const override;
 
 	virtual bool Visit(const DatabaseSelection &selection,
 			   VisitDirectory visit_directory,

src/filter/ChainFilterPlugin.cxx

@@ -52,10 +52,11 @@ public:
 		children.emplace_back(name, filter);
 	}
 
-	virtual AudioFormat Open(AudioFormat &af, Error &error) override;
-	virtual void Close();
-	virtual const void *FilterPCM(const void *src, size_t src_size,
-				      size_t *dest_size_r, Error &error);
+	/* virtual methods from class Filter */
+	AudioFormat Open(AudioFormat &af, Error &error) override;
+	void Close() override;
+	const void *FilterPCM(const void *src, size_t src_size,
+			      size_t *dest_size_r, Error &error) override;
 
 private:
 	/**

src/filter/NormalizeFilterPlugin.cxx

@@ -34,10 +34,11 @@ class NormalizeFilter final : public Filter {
 	PcmBuffer buffer;
 
 public:
-	virtual AudioFormat Open(AudioFormat &af, Error &error) override;
-	virtual void Close();
-	virtual const void *FilterPCM(const void *src, size_t src_size,
-				      size_t *dest_size_r, Error &error);
+	/* virtual methods from class Filter */
+	AudioFormat Open(AudioFormat &af, Error &error) override;
+	void Close() override;
+	const void *FilterPCM(const void *src, size_t src_size,
+			      size_t *dest_size_r, Error &error) override;
 };
 
 static Filter *

src/filter/ReplayGainFilterPlugin.cxx

@@ -116,10 +116,11 @@ public:
 	 */
 	void Update();
 
-	virtual AudioFormat Open(AudioFormat &af, Error &error) override;
-	virtual void Close();
-	virtual const void *FilterPCM(const void *src, size_t src_size,
-				      size_t *dest_size_r, Error &error);
+	/* virtual methods from class Filter */
+	AudioFormat Open(AudioFormat &af, Error &error) override;
+	void Close() override;
+	const void *FilterPCM(const void *src, size_t src_size,
+			      size_t *dest_size_r, Error &error) override;
 };
 
 void

src/filter/RouteFilterPlugin.cxx

@@ -120,10 +120,11 @@ public:
 	 */
 	bool Configure(const config_param &param, Error &error);
 
-	virtual AudioFormat Open(AudioFormat &af, Error &error) override;
-	virtual void Close();
-	virtual const void *FilterPCM(const void *src, size_t src_size,
-				      size_t *dest_size_r, Error &error);
+	/* virtual methods from class Filter */
+	AudioFormat Open(AudioFormat &af, Error &error) override;
+	void Close() override;
+	const void *FilterPCM(const void *src, size_t src_size,
+			      size_t *dest_size_r, Error &error) override;
 };
 
 bool

src/filter/VolumeFilterPlugin.cxx

@@ -57,10 +57,10 @@ public:
 		volume = _volume;
 	}
 
-	virtual AudioFormat Open(AudioFormat &af, Error &error) override;
-	virtual void Close();
-	virtual const void *FilterPCM(const void *src, size_t src_size,
-				      size_t *dest_size_r, Error &error);
+	AudioFormat Open(AudioFormat &af, Error &error) override;
+	void Close() override;
+	const void *FilterPCM(const void *src, size_t src_size,
+			      size_t *dest_size_r, Error &error) override;
 };
 
 static constexpr Domain volume_domain("pcm_volume");