[SECURITY] Protect Mailtransport

Fix CVE-2016-10074 by disallowing potentially unsafe shell characters.

Resolves: #79114
Releases: master, 8.5, 7.6, 6.2
Change-Id: I8578b63c8c571964c2d52a65e4bfbf705c20f816
Reviewed-on: https://review.typo3.org/51093


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Alexander Opitz <opitz.alexander@googlemail.com>
Tested-by: Alexander Opitz <opitz.alexander@googlemail.com>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>