[BUGFIX] Always use slashes in paths

In the check to see if a translation for a system extension
is downloaded the path to the extension is checked if it contains
'sysext'. In this check forward slashes must be used instead of
DIRECTORY_SEPARATOR (even on Windows).

Resolves: #70717
Releases: master
Change-Id: I7c84b3f49e0a9199098f84c3e0ee52e08a8f87c9
Reviewed-on: http://review.typo3.org/44063


Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Simon Schaufelberger <simonschaufi@googlemail.com>
Tested-by: Simon Schaufelberger <simonschaufi@googlemail.com>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>