Backports php5.6

[lode]

Do not merge into master. To use in Respondens, merge into release-editor.

This is a continuous PR backporting upstreams master to php5.

To bring up-to-date with upstream changes:

• git fetch --all --prune
• git checkout master
• git merge upstream/master
• git push
• git checkout backports-php5.6
• git merge master
• You'll probably get conflicts, don't try to solve them, instead:
  • git checkout --theirs .
  • Do not commit, instead continue
• Run the steps as documented in PHP5_TRANSPILATION.md
• rm .php-cs-fixer.cache
• ./vendor/bin/phpunit tests (don't proceed if there are failures which are not there on master)
• git add .
• git commit
• git push