This was triggered by innodb.innodb_multi_update, where we had a static length row without nulls and xtradb didn't fill in the delete-marker byte


include/my_bitmap.h:
  Added prototype for bitmap_union_is_set_all()
mysys/my_bitmap.c:
  Added function to check if union of two bit maps covers all bits.
sql/mysql_priv.h:
  Updated protype for compare_record()
sql/sql_insert.cc:
  Send to compare_record() flag if all fields are used.
sql/sql_select.cc:
  Set share->null_bytes_for_compare.
sql/sql_update.cc:
  In compare_record() don't use the fast cmp_record() (which is basically memcmp) if we don't know that all fields exists.
  Don't compare the null_bytes if there is no data there.
sql/table.cc:
  Store in share->null_bytes_for_compare the number of bytes that has null or bit fields (but not delete marker)
  Store in can_cmp_whole_record if we can use memcmp() (assuming all rows are read) to compare rows in compare_record()
sql/table.h:
  Added two elements in table->share to speed up checking how updated rows can be compared.