heimdal -- bypass of capath policy

Viktor Dukhovni reports:

Commit f469fc6 (2010-10-02) inadvertently caused the
previous hop realm to not be added to the transit path of issued
tickets. This may, in some cases, enable bypass of capath policy in
Heimdal versions 1.5 through 7.2. Note, this may break sites that rely
on the bug. With the bug some incomplete [capaths] worked, that should
not have. These may now break authentication in some cross-realm
configurations. (CVE-2017-6594)