bug #46947 "Embedded SELECT without FOR UPDATE is causing 
a lock".

Fixed comments in tests. Improved comments and performance of
auxiliary scripts.

mysql-test/include/check_concurrent_insert.inc:
  Changed script to use temporary table for backing up data in
  order to make this operation less expensive. Made script more
  a bit generic by allowing to use multi-column tables with it.
  Improved comments.
mysql-test/include/check_no_concurrent_insert.inc:
  Changed script to use temporary table for backing up data in
  order to make this operation less expensive. Made script more
  a bit generic by allowing to use multi-column tables with it.
  Improved comments.
mysql-test/include/check_no_row_lock.inc:
  Improved comments in auxiliary script.
mysql-test/r/innodb_mysql_lock2.result:
  Fixed errors in comments for test.
mysql-test/r/lock_sync.result:
  Fixed typo in comments for test.
mysql-test/t/innodb_mysql_lock2.test:
  Fixed errors in comments for test.
mysql-test/t/lock_sync.test:
  Fixed typo in comments for test.