Cannot correctly handle filenames with "：" (U+FF1A full-width colon)

[ncw (Nick Craig-Wood)]

@ivandeex

I wonder if we could add a central variable encode.WideChars = keep|none in lib/encode to make it silently skip all wide-to-half character translations but asymmetrically continue opposite half-to-wide translation,

This scheme has the potential for clashes given that multiple files locally may map to one file remotely.

That probably wouldn't be a problem for Windows though, but might be for Linux.