set.

(Ramil's patch, recreated.)


heap/hp_delete.c:
  Reset info->lastkey_len for further heap_rnext/heap_rprev calls.
mysql-test/r/heap_btree.result:
  Test for bug #9719: DELETE with WHERE on HEAP table just deletes first 
  row of matched set.
mysql-test/t/heap_btree.test:
  Test for bug #9719: DELETE with WHERE on HEAP table just deletes first 
  row of matched set.