Add support for UTF-16 strings for LowPaths in FS:USER

```
23:23:42]  <+yuriks>	archshift: UTF16toUTF8 in string_util.h
[23:23:51]  <+yuriks>	though it should be fixed to use u16_string instead
[23:23:56]  <+yuriks>	or we can just rewrite it :D
[23:24:04]  <+yuriks>	cause we probably don't need all the other cruft
```

@bunnei, @neobrain: thoughts?