Add Windows support

[mdedetrich]

scala.tools.jardiff.IOUtilSpec is failing on Windows and it appears that scala.tools.jardiff.IOUtil.rootPath needs to be changed so its Windows aware, see #152 (comment)

[He-Pin]

I'm using windows, and I can take a look at this one.

[SethTisue]

@He-Pin any luck?

[SethTisue]

@mdedetrich this isn't a regression, is it?

[mdedetrich]

@mdedetrich this isn't a regression, is it?

Afaik it's not a regression, it just never worked on Windows

[som-snytt]

I also never worked on Windows.