(similar to {@link col_full_name()})
X::dump($db->cfn("name", "table_users"));
// (string) table_users.name
X::dump($db->cfn("name", "table_users", true));
// (string) \`table_users\`.\`name\`
function(string $col, string $table = NULL, bool $escaped = false)
{
return $this->colFullName($col, $table, $escaped);
}