Update custom_constraint.rst
bug #4390 Update custom_constraint.rst (luciantugui)

This PR was merged into the 2.5 branch.

Discussion
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Update custom_constraint.rst

Commits
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5f8b13c Update custom_constraint.rst
Revert "Revert "Added config example for Varnish 4.0""

This re-adds PR #4280, which was temporarily reverted while we waited
for the proper PHP extensions.
Merge branch '2.3' into 2.5

* 2.3:
  Revert "Revert "Added config example for Varnish 4.0""
Merge branch '2.5'

* 2.5:
  Revert "Revert "Added config example for Varnish 4.0""
  Update custom_constraint.rst