Bug#24388746: PRIVILEGE ESCALATION AND RACE CONDITION USING CREATE TABLE

During REPAIR TABLE of a MyISAM table, a temporary data file (.TMD)
is created. When repair finishes, this file is renamed to the original
.MYD file. The problem was that during this rename, we copied the
stats from the old file to the new file with chmod/chown. If a user
managed to replace the temporary file before chmod/chown was executed,
it was possible to get an arbitrary file with the privileges of the
mysql user.

This patch fixes the problem by not copying stats from the old
file to the new file. This is not needed as the new file was
created with the correct stats. This fix only changes server
behavior - external utilities such as myisamchk still does
chmod/chown.

No test case provided since the problem involves synchronization
with file system operations.