Issue #1267508 by fietserwin, daffie, lisa.ugray, chx, alexpott, Berdir, dawehner, Crell: Subselects don't work in DBTNG conditions, except when used as value for IN

Revert "Issue #1267508 by fietserwin, lisa.ugray, daffie, chx, Crell: Subselects don't work in DBTNG conditions, except when used as value for IN"

This reverts commit 22a241ca.

Issue #1267508 by fietserwin, lisa.ugray, daffie, chx, Crell: Subselects don't work in DBTNG conditions, except when used as value for IN

Issue #2713831 by vegantriathlete, lisa.ugray, joshi.rohit100, jhodgdon, deviantintegral, kellyimagined, alexpott, akalata, soulsesa: Document #machine_name exists parameters

Issue #2722265 by willito, kellyimagined, joachim, hussainweb, munizjor, selfuntitled, lisa.ugray, soulsesa, The Sean, kjl16, kurthill4: docs for MailManager::mail() refer to obsolete function user_preferred_langcode()