Issue #1923406 by stefan.r, yannickoo, catch, Crell, amateescu, pwolanin, morgantocker, Damien Tournoud, sun: Use ASCII character set on alphanumeric fields so we can index all 255 characters

Revert "Issue #1923406 by stefan.r, yannickoo: Use ASCII character set on alphanumeric fields so we can index all 255 characters"

This reverts commit ac4e35ce.

Issue #1923406 by stefan.r, yannickoo: Use ASCII character set on alphanumeric fields so we can index all 255 characters

Issue #2466917 by jhedstrom: DatabaseCacheTagsChecksum::calculateChecksum() has incorrect documentation

Issue #2358079 by pwolanin, Berdir: Require a specific placeholder format in db_query() in order to trigger argument expansion, and require explicit 'IN' parameter for conditions