interactive cannot process cursor properly when wide character is included.

[yjh0502]

I try to use Korean in node interactive(REPL), but it cannot process cursor properly.
It interpret all characters with same width, but some eastern character is twice more wide than common characters.

for example, if I enter

a = '안녕하세요'

than cursor places just after '하'.

[ry]

https://github.com/ry/node/blob/e1f4b3f009db6b80a4fb136926caba8a788ab7f8/TODO#L3