Merge branch 'revert-ca7c77d9' into 'stable-3.1'
Revert "Update apache_ispconfig.vhost.master" See merge request !823
I believe this change is incorrect, I get a syntax error with the "add" left in.
The issue in https://www.howtoforge.com/community/threads/email-settings.80255/#post-380283 is likely the version of apache in centos6, which a web search says is 2.4.6, and SetIfEmpty was added in 2.4.7. A better fix would be an check, using 'set' if < 2.4.7 and 'setifempty' otherwise.