Make XML report output well formed.

The XML report output is not standards compliant now and will not work with correctly implemented XML parsers.

Added <?xml header, even though many parsers may work without it, better to have it.
Added a dirty hack to rename Loss% tag to just Loss, as % is not allowed in tag names (http://www.w3.org/TR/REC-xml/#sec-common-syn).
Added quotes around attribute names, as quotes are mandatory (http://www.w3.org/TR/REC-xml/#NT-AttValue).

If you know or think anyone is using the current format, I can add an option for selecting well-formed output.