Bring back the nice LineEditREPL on Windows

Windows doesn't have the TERM env var set outside of MSYS/Cygwin, so c8ae026c557 caused Windows Julia to default to the BasicREPL.

The LineEditREPL still has line duplication bugs on Windows (https://github.com/JuliaLang/julia/issues/6488), but overall it's a nicer experience than the BasicREPL.

This may un-fix https://github.com/JuliaLang/julia/issues/6428 on Windows, but I suspect Windows users are more frequently running Julia from cmd or by double-clicking than inside Emacs.