Bug#474609: Netrw's handling of multi-byte filepaths

[drchip at campbellfamily.biz]

Hello!

As you might surmise, I don't use multi-byte filenames or directory names.  I
figured out how to make them, though, so I was able to test this problem.

v125h tries to address this; it involved changing various places which used to
use s:Strlen() (but not all).  There's a new option variable, too:
g:netrw_xstrlen.  Haven't documented it (yet), but it allows one to choose
several methods to figure out multi-character string lengths.  However, the
problem you forwarded involved a need to use the actual string length, not the
visible string length.  Hopefully I got all the changes right for this.

Regards,
Chip Campbell