Unicode filenames

[judah]

We should probably support Unicode filenames for the history and preferences files (as well as in runFileInputT). Perhaps this should just wait for ghc-6.12's Unicode filename support rather than implementing it ourselves (see also #20).

[judah]

Now that Haskeline provides encoding functionalities, it's probably worth implementing this ourselves.

Annoyingly, System.Console.Haskeline.Completion doesn't have access to the RunTerm with the encoders.

Probably the best solution is a separate hidden module System.Console.Haskeline.Directory with #ifdefs that imports the various Backend submodules directly. This would mean that on Cygwin we'd use the Win32 encoding, but that might not be such a bad thing (and anyway, Cygwin isn't supported enough for that to matter yet).