work around file-io not setting locale encoding when opening a Handle

work around file-io not setting locale encoding when opening a Handle

Works around this bug https://github.com/haskell/file-io/issues/45

The fix is in Utility.FileIO.CloseOnExec because all use of file-io is
already wrapped through that module. Although perhaps that ought to be
refactored at this point.

I'd hope that file-io will eventually fix this bug, and also provide
CloseOnExec variants of its functions. That would allow depending on the
fixed version, and removing this ugly code.

Note that, functions like readFile that don't care about the encoding
due to reading/writing a ByteString were kept optimally fast by not
setting the encoding. This avoids an IORef read and write per open.

Sponsored-by: Graham Spencer