Correct env TEMP var for Windows

The Windows environment var for temp stuff is TEMP or TMP.  As coded, on Windows, findSuitableTempdirectory always created a tmp directory on the root of the current drive.  Not all users can do this, leading to possible permissions issues.  The change picks up a more correct env var.
Merge pull request #115 from gbloice/master

Correct env TEMP var for Windows