Currently:
  * builds leak files into these directories
  * builds that crash or leak handles sometimes leak locks between multiple builds on the same machine. Since all builds currently share the same tempdir, this means that leaked lockfiles or simply having files opened on windows causes issues between builds
  * no clean way to 'clean' the tempdir; currently we use a big hammer that does a 'try to delete everything and hope for the best' pass on temp

The solution here is to have the builders set unique values for the various temp environment variables before running the task. Additionally, when the task starts, they'll attempt to delete any existing temporary directories that were leftovers.