.......PS. [ZBXNEXT-207] added the runtime control option to force execution of housekeeper

git-svn-id: svn://svn.zabbix.com/trunk@50157 f4e7fd02-d210-4e34-a1e0-d4093fb66cc2
.......... [ZBXNEXT-826] updated release version [2.2.8rc1]; updated API version [2.2.8]

git-svn-id: svn://svn.zabbix.com/trunk@50158 f4e7fd02-d210-4e34-a1e0-d4093fb66cc2
........S. [ZBX-6353] improved history cache performance when it's flooded with data from less than 1000 items
           [merge ^/branches/2.4 -c r50159]


git-svn-id: svn://svn.zabbix.com/trunk@50160 f4e7fd02-d210-4e34-a1e0-d4093fb66cc2