interpret pluginName as UTF8 rather than pure ASCII
interpret pluginName as UTF8 rather than pure ASCII

toUnicode is just expanding bytes to short, and re-interpret them UTF16, not regarding original encoding.
This works well for pure ASCII, but is not really defined for other encodings.
We should prefer using UTF8 by default for all the image-VM string transfer.

OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,OpenSmalltalk/vm,timfel/squeakvm,timfel/squeakvm,OpenSmalltalk/vm,OpenSmalltalk/vm