- removed Win32-only IOErrorType.ComError
- added IOErrorType.(DynIOError Dynamic.Dynamic)

  Propagating dynamically-typed exceptions as Exception.DynException
  isn't always the right thing to do
  [ why? You cannot catch them with IO.catch & you don't get the
    'infrastructure' that IOError offers, so you're forced to
    reinvent that wheel for each dynamic exception.
  ]
- removed IOExts.isComError  :: IOError -> Bool
- added IOExts.isDynIOError  :: IOError -> Bool
- added IOExts.getDynIOError :: IOError -> Dynamic.Dynamic
- documented IOExts changes.