Help: Don't use tmpfile() on windows

On windows, tmpfile() places the file in the root directory, which is protected on recent versions of Windows.

Use _tempnam to place the temporary file in TMP instead.

On other OS, continue to use tmpfile().
Merge branch 'master' into KDP
KDP: Provide real help

Replace the help string used for debugging the HELP facility with help for the KDP device.

Move introductory comment block into help.