ThreadScope shows garbled characters when using Unicode characters in user event

**Original reporter**: _shelarcy_

Debug.Trace.traceEventIO output Unicode characters by UTF-8 String.
- http://www.haskell.org/ghc/docs/7.4.1/html/libraries/base-4.5.0.0/Debug-Trace.html#v:traceEventIO

"ghc-events show" can show output Unicode characters' user event correctly.

```
import Debug.Trace
main = do
traceEventIO "テスト"
putStrLn "test"
```

```
$ ghc -O2 -threaded -eventlog Test.hs
[1 of 1] Compiling Main ( Test.hs, Test.o )
Linking Test.exe ...

$ .\Test.exe +RTS -l
"test"
$ ghc-events show Test.eventlog > test.log
```

```
Event Types:
(snip)

Events:
(snip)
1531003: cap 0: running thread 3
1594090: cap 0: テスト
1805086: cap 0: stopping thread 3 (making a foreign call)
(snip)
```

But ThreadScope can't show Unicode characters' user event correctly. ThreadScope shows garbled characters.

This is bad. Unicode character is useful to find user event for me.

I'm using GHC 7.4.1 with threadscope 0.2.1 and gtk 0.12.3, on Windows.