Windows file names don't work correctly

There are a couple of spots in the utility code that mistakenly see the colon in a windows file name (c:\foo\bar\...) as a URL instead of a file name.  We also need to use the Unix file name conventions when adding `@base` and the like into the turtle parser.  Note that the `windows_bug` branch has a first approximation of one of the fixes.

[] bug fixes in
[] add windows VM to the test harness 