* application-src/amgtar.c: Output message for selfcheck
* client-src/client_util.c (backup_support_option): Parse
  "MESSAGE-JSON".
* client-src/client_util.h (backup_support_option_s): Add message_json.
* client-src/selfcheck.c: Parse message from application.
* common-src/ammessage.c: Add amgtar message.
* perl/Amanda/Extract.pm (BSU): parse message-json
* perl/Amanda/Message.pm: Add amgtar message (3700000).
* server-src/amcheck.c: Remove unused code, small cleanup.
* installcheck/Installcheck/Application.pm (selfcheck_message):
  execute application selfcheck with '--message json'.
* installcheck/amgtar.pl: Call selfcheck_message.



git-svn-id: https://svn.code.sf.net/p/amanda/code/amanda/trunk@5947 a8d146d6-cc15-0410-8900-af154a0219e0