SERVER-6086 linenoise handles backspace incorrectly with Korean character set

 - use mk_wcswidth before refresh line. for calculate width.
Sounds good.

Can you make the argument types consistent with dynamicReferesh? ie. UChar* buf32, int n.

```
static void dynamicRefresh( PromptBase& pi, UChar32* buf32, int len, int pos ) {
```