Check UTF-8 variables / input data are displayed correctly

[shabble]

/JOIN #평범한대화방 appears to display incorrectly in uberprompt as "[ImaginaryNet/#평범한대?]"

Confirm that utf-8 is being properly handled by the script, and that it's either an Irssi problem (c.f
unicode/colours in sbar items bug and sbar string length bug), or that it can and should be fixed.

[ailin-nemui]

irssi bug with $[...]variable, may be good for uberprompt to do this itself

[ailin-nemui]

irssi bug is now fixed in irssi/irssi#480