BUG#42150: binlog_start_comment.test failed: Error writing file 'UNOPENED'
BUG#42150: binlog_start_comment.test failed: Error writing file 'UNOPENED'

NOTE: backporting BUG#42150 into next-mr
      Includes latest Andrei's patch (see [2 Feb 18:40] Bugs System)
      and merge.test post-push fix (see [3 Feb 18:04] Bugs System)

The reason of the bug appeared to be overreacting on absense of a
binlog file although the file name had been presented in in the master
binlog index file.
By convention, there should have been only a warning printed and the rest of
`reset master' logics completed.  This did not happen on windows
due to incorrect value of my_errno returned from nt_share_delete().
      
Fixed with correcting my_errno assignment in nt_share_delete() to be ENOENT in 
he event of no binlog file. Some minor refactoring has been made.
natsys/mariadb_10.2,ollie314/server,natsys/mariadb_10.2,ollie314/server,ollie314/server,natsys/mariadb_10.2,ollie314/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,ollie314/server,flynn1973/mariadb-aix,davidl-zend/zenddbi,ollie314/server,ollie314/server,natsys/mariadb_10.2,flynn1973/mariadb-aix,davidl-zend/zenddbi,natsys/mariadb_10.2,davidl-zend/zenddbi,flynn1973/mariadb-aix,davidl-zend/zenddbi,ollie314/server,davidl-zend/zenddbi,natsys/mariadb_10.2,natsys/mariadb_10.2,davidl-zend/zenddbi,ollie314/server,flynn1973/mariadb-aix,flynn1973/mariadb-aix,davidl-zend/zenddbi,slanterns/server,davidl-zend/zenddbi,flynn1973/mariadb-aix,davidl-zend/zenddbi,flynn1973/mariadb-aix,flynn1973/mariadb-aix,ollie314/server,flynn1973/mariadb-aix,davidl-zend/zenddbi,ollie314/server,davidl-zend/zenddbi,flynn1973/mariadb-aix,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2