Zabbix

........S. [ZBX-13225] fixed curl version check

For the elasticsearch back-end to work, we need libCURL >= 7.28.0.
This is due to the face that we use curl_multi_wait(), that
was introduced in that version.
This fix compilation problem on all the platforms that lack
a newer version of libCURL that zabbix still support.

[svn merge -c 76217 ^/branches/3.4]

Resolved conflict:
	src/libs/zbxhistory/history_elastic.c