make file extensions lowercase before comparing them

src/browser.cpp

@@ -53,6 +53,7 @@ namespace
 			return false;
 		
 		string ext = file.substr(last_dot+1);
+		ToLower(ext);
 		for (int i = 0; supported_extensions[i] != "."; i++)
 			if (ext == supported_extensions[i])
 				return true;

src/tag_editor.cpp

@@ -301,6 +301,7 @@ bool GetSongTags(Song &s)
 	
 	string ext = s.GetFile();
 	ext = ext.substr(ext.find_last_of(".")+1);
+	ToLower(ext);
 	
 	mTagEditor->Clear();
 	mTagEditor->Reset();
@@ -356,6 +357,7 @@ bool WriteTags(Song &s)
 		
 		string ext = s.GetFile();
 		ext = ext.substr(ext.find_last_of(".")+1);
+		ToLower(ext);
 		if (ext == "mp3")
 		{
 			MPEG::File file(path_to_file.c_str());