Fix ftp utf8 problem by add an 'utf8' option for ftp url.

it's an old problem of xbmc ftp module: http://forum.xbmc.org/showthread.php?tid=121478

but it indeed is a bug of xbmc, since we read file list from ftp server and we should send the filename back to ftp server in same encoding the server send to us.

here's an easy fix for it, since the utf-8 is the most likely used and supported encoding of current world running ftp servers, we should support utf-8 encoding in a safe way.

so I added an 'utf8' option for ftp url, when adding ftp source, user can input it as part of the url or path, e.g. ftp://user:pwd@serveraddr:port/path/?utf8=1

then the all subdir/files of the url source will has the utf8 option value "1", which will tell CurlFile send out the file path/name without conversion (we are using utf8 in xbmc).