Backport of subquery optimizations to 5.3.

There are still test failures because of:
- Wrong query results in outer join + semi join
- EXPLAIN output differences

sql/structs.h

@@ -123,6 +123,21 @@ struct st_read_record;				/* For referense later */
 class SQL_SELECT;
 class THD;
 class handler;
+class Copy_field;
+
+/**
+  A context for reading through a single table using a chosen access method:
+  index read, scan, etc, use of cache, etc.
+
+  Use by:
+  READ_RECORD read_record;
+  init_read_record(&read_record, ...);
+  while (read_record.read_record())
+  {
+    ...
+  }
+  end_read_record();
+*/
 
 typedef struct st_read_record {			/* Parameter to read_record */
   struct st_table *table;			/* Head-form */
@@ -140,6 +155,12 @@ typedef struct st_read_record {			/* Parameter to read_record */
   uchar	*cache,*cache_pos,*cache_end,*read_positions;
   IO_CACHE *io_cache;
   bool print_error, ignore_not_found_rows;
+  /* 
+    SJ-Materialization runtime may need to read fields from the materialized
+    table and unpack them into original table fields:
+  */
+  Copy_field *copy_field;
+  Copy_field *copy_field_end;
 } READ_RECORD;