DELETE statement

Single-table delete ordered by a field that has a hash-type index
may cause an assertion failure or a crash.

An optimization added by the fix for the bug 36569 forced the
optimizer to use ORDER BY-compatible indices when applicable.

However, the existence of unsorted indices (HASH index algorithm
for some engines such as MEMORY/HEAP, NDB) was ignored.

The test_if_order_by_key function has been modified to skip
unsorted indices.


mysql-test/r/heap_hash.result:
  Test case for bug #55472.
mysql-test/t/heap_hash.test:
  Test case for bug #55472.
sql/sql_select.cc:
  Bug #55472: Assertion failed in heap_rfirst function of hp_rfirst.c on
              DELETE statement
  
  The test_if_order_by_key function has been modified to skip
  unsorted indices.