Issue #1650930 by mkalkbrenner, gidarai, daffie, JeroenT, murilohp, jungle, acbramley, shahankitb1982, anmolgoyal74, claudiu.cristea, klausi, super_romeo, ankithashetty, longwave, pooja saraah, sahil.goyal, mikeytown2, deviantintegral, mhavelant, elgandoz, catch, andypost, pounard, neclimdul, Damien Tournoud, Charlie ChX Negyesi, danblack, larowlan: Use READ COMMITTED by default for MySQL transactions

Issue #1650930 by mkalkbrenner, gidarai, daffie, JeroenT, murilohp, jungle, acbramley, shahankitb1982, anmolgoyal74, claudiu.cristea, klausi, super_romeo, ankithashetty, longwave, pooja saraah, sahil.goyal, mikeytown2, deviantintegral, mhavelant, elgandoz, catch, andypost, pounard, neclimdul, Damien Tournoud, Charlie ChX Negyesi, danblack, larowlan: Use READ COMMITTED by default for MySQL transactions

Issue #2232425 followup by danblack, stefan.r: Fixed Database Schema field/column default value is not properly quoted via PDO::quote().

Issue #2224847 by pwolanin, damiankloip, danblack, Berdir: Fixed Automatically shorten cid's in Cache\DatabaseBackend and PhpBackend.

Issue #2232425 by danblack: Database Schema field/column default value is not properly quoted via PDO::quote().

Issue #1969108 by danblack, jhodgdon: INSTALL.mysql.txt does not mention CREATE TEMPORARY TABLES and it should.