V6 backports

[kinkie]

Backporting commits:

• 8b31858 : Portability: remove explicit check for libdl
• dd3292c : Refactor peerRefreshDNS() to clarify its (void*)1 logic
• 0ef767a: Nil request dereference in
  ACLExtUser and SourceDomainCheck ACLs

[yadij]

@kinkie, this being a backport of multiple changes it is destined for a rebase-merge instead of a squash-merge. That means edits like these review changes and build fixes need to be manually combined in the PR branch.

if you were not aware how to do that:

• In your branch checkout run:
  • git rebase -i v6
• In the editor that comes up:
  • reorder the fixes underneath the commit they change
  • replace action (first character) p with f

N.B. Ideally manual backports are separate PRs to avoid this type of tricks.

[kinkie]

@kinkie, this being a backport of multiple changes it is destined for a rebase-merge instead of a squash-merge. That means edits like these review changes and build fixes need to be manually combined in the PR branch.

if you were not aware how to do that:

• In your branch checkout run:

  • git rebase -i v6

• In the editor that comes up:

  • reorder the fixes underneath the commit they change
  • replace action (first character) p with f

N.B. Ideally manual backports are separate PRs to avoid this type of tricks.

Thanks for the advice, and yes I'll do individual backports next time