FileSystem.hxx: add FOpen modes for appending files
Path.hxx: add GetDirectoryName() method
ConfigFile.cxx: use FOpenMode
ExcludeList.cxx: use FOpen
PlaylistFile.cxx: use file system API
PlaylistSave.cxx: use FOpen
SongUpdate.cxx: use StatFile
TextFile.hxx: use file system API
UpdateWalk.cxx: use FileExists
UpdateIO.cxx: use file system API, log in UTF-8
SimpleDatabasePlugin: use file system API, log in UTF-8
StateFile: use file system API, log in UTF-8