Removed unused class Future
Tweaked DllImport CharSets
Turned immutable Comparers into Singletons
Improved ITask and ITaskHandler XML comments
CopyDirectory: Remove Hidden file attribute in addition to ReadOnly attribute

Samba shares implicitly mark dot files as Hidden, potentially causing problems when copying/overwriting
Extracted LanguageSet.KnownLanguages to Languages.AllKnown

Removing this from LanguageSet avoids unnecessary execution of the static constructor when we want to create a LanguageSet but do not need a list of all languages.
Added FileUtils.IsUnifxFS()
Tweaked DownloadFile