misc/amanda-server: update to 3.5.1

• define LICENSE
• simplify handling of USERS and GROUPS
• reorder make variables in accordance with policy
• regenerate patches
• harden amstatus against task death

Changelog: https://www.zmanda.com/amanda-community/?ss360SearchTerm=3.5.1

PR: 264714
Approved by: fbsd@dylanleigh.net (maintainer timeout)