Added page_range to records_in_range() to improve range statistics

Prototype change:
-  virtual ha_rows records_in_range(uint inx, key_range *min_key,
-                                   key_range *max_key)
+  virtual ha_rows records_in_range(uint inx, const key_range *min_key,
+                                   const key_range *max_key,
+                                   page_range *res)

The handler can ignore the page_range parameter. In the case the handler
updates the parameter, the optimizer can deduce the following:
- If previous range's last key is on the same block as next range's first
  key
- If the current key range is in one block
- We can also assume that the first and last block read are cached!
  This can be used for a better calculation of IO seeks when we
  estimate the cost of a range index scan.

The parameter is fully implemented for MyISAM, Aria and InnoDB.
A separate patch will update handler::multi_range_read_info_const() to
take the benefits of this change and also remove the double
records_in_range() calls that are not anymore needed.

sql/opt_range.cc

@@ -6724,6 +6724,7 @@ static double ror_scan_selectivity(const ROR_INTERSECT_INFO *info,
     {
       /* create (part1val, ..., part{n-1}val) tuple. */
       ha_rows records;
+      page_range pages;
       if (!tuple_arg)
       {
         tuple_arg= scan->sel_arg;
@@ -6741,7 +6742,7 @@ static double ror_scan_selectivity(const ROR_INTERSECT_INFO *info,
       min_range.length= max_range.length= (uint) (key_ptr - key_val);
       min_range.keypart_map= max_range.keypart_map= keypart_map;
       records= (info->param->table->file->
-                records_in_range(scan->keynr, &min_range, &max_range));
+                records_in_range(scan->keynr, &min_range, &max_range, &pages));
       if (cur_covered)
       {
         /* uncovered -> covered */