[BUGFIX] Ensure unix like paths for temp files

Using tempnam() on Windows systems returns paths containing backslashes.
As other paths inside the core are already transformed to paths using
forward slashes some string comparisons fail. This patch ensures correct
transforming of slashes after the usage of tempnam().

Releases: master, 6.2
Resolves: #64682
Change-Id: Ic85e06d9ed32c9f668efd5bb74b9bc14df367e1b
Reviewed-on: http://review.typo3.org/36493


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Mateusz Wojtuła <matw88@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>