Uses svn info --xml, includes repo and revision, other tweaks

I have been learning a little powershell and playing with posh-svn at the same time. I thought you might be interested in some of what I've done.

- Normalize paths to account for mis-entered case
- Use structure XML output from svn info
- Include repository and revision details in the prompt (this has some problems still)
- Integrate with posh-hg and posh-git (still not sure I've done this in the best way)