Added open log file with FILE_SHARE_DELETE flag on Windows.

sql/log.cc:
  added reopen_fstreams();
  modified redirect_std_streams(): call to sequence of freopen()
  replaced to reopen_fstreams();
  modified flush_error_log(): removed file rename for flushed
  error log file.
sql/mysqld.cc:
  modified main() and init_server_components(): do open log error file
  over call to reopen_fstreams().