Zabbix

A......... [ZBX-13789] improved performance of "Problems" widget with MySQL backend by removing DISTINCT modifier from SQL statements with tables joined by primary keys

* commit 'cda55ece5df297a01f7917f5b52b78a0b2238cc8':
  .D........ [ZBX-13789] added ChangeLog entry
  A......... [ZBX-13789] removed DISTINCT modifier from SQL statements with tables joined by primary keys
  A......... [ZBX-13789] fixed coding style issues discovered during code review: moved zbx_db_distinct() function to CApiService class
  A......... [ZBX-13789] fixed coding style issues discovered during code review: made createSelectQueryFromParts() method static