…le (javiereguiluz)

This PR was submitted for the 2.8 branch but it was merged into the 2.7 branch instead (closes #7509).

Discussion
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Added a mention to APCu Polyfill in the performance article

This fixes #6827.

Commits
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0b38670 Added a mention to APCu Polyfill in the performance article

* 2.7: (30 commits)
  [#7560] remove unused use statements
  Resolving $this usage outside a class on form.rst
  Fix some odd English in the PDOSessionHandler docs
  Fix typo
  Add the description for the HTTP status because it's not that common
  Update exception code status
  [#7592] some minor tweaks
  Fix link for Twig Extensions documentation
  Update framework.rst [Fix esi tag]
  Update render_without_controller.rst
  Update matchers.rst
  Update matchers.rst
  Update locale_sticky_session.rst
  Update framework.rst
  Update import.rst
  Update load_balancer_reverse_proxy.rst
  Moved the requirements file
  [#7509] add missing references
  Added a mention to APCu Polyfill in the performance article
  [#7497] minor rewording
  ...