DSA-3861 libtasn1-6 - security update

Jakub Jirasek of Secunia Research discovered that libtasn1, a library
used to handle Abstract Syntax Notation One structures, did not
properly validate its input. This would allow an attacker to cause a
crash by denial-of-service, or potentially execute arbitrary code, by
tricking a user into processing a maliciously crafted assignments
file.