[dovecot/core] 5714c4: acl: Add acl_globals_only setting

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/dovecot/core
  Commit: 5714c480bb705939ef33de2ec7e8fb501809aa49
      https://github.com/dovecot/core/commit/5714c480bb705939ef33de2ec7e8fb501809aa49
  Author: Timo Sirainen <timo.sirainen at dovecot.fi>
  Date:   2017-06-19 (Mon, 19 Jun 2017)

  Changed paths:
    M src/plugins/acl/acl-api-private.h
    M src/plugins/acl/acl-backend-vfile.c
    M src/plugins/acl/acl-backend.c

  Log Message:
  -----------
  acl: Add acl_globals_only setting

The local dovecot-acl files aren't even attempted to be looked up if this is
set. This is mainly useful to avoid unnecessary stat()s to dovecot-acl files
that never exist.