Fix to correct behaviour of find_and_fetch_row() for tables that have primary keys stored
in storage engines that support the fast method to fetch rows given a primary key. The
method uses position() to retrieve the key for a given record and rnd_pos() to position
the internal "cursor" at the row. Rnd_pos() returns the found record in table->record[0],
so the record has to be moved to table->record[1] for further processing after calling
find_and_fetch_row().


sql/log_event.cc:
  Adding code to one exit branch of find_and_fetch_row() to move output record from
  table->record[0] to table->record[1].
  Adding function to do valgrind memory check.
  Adding valgrind memory checks to check that records are defined when they should be.
  Adding Doxygen comment to find_and_fetch_row() with pre- and post-conditions.