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.

storage/spider/spd_db_mysql.cc

@@ -12690,8 +12690,8 @@ int spider_mbase_handler::append_truncate(
 }
 
 int spider_mbase_handler::append_explain_select_part(
-  key_range *start_key,
-  key_range *end_key,
+  const key_range *start_key,
+  const key_range *end_key,
   ulong sql_type,
   int link_idx
 ) {
@@ -12714,8 +12714,8 @@ int spider_mbase_handler::append_explain_select_part(
 
 int spider_mbase_handler::append_explain_select(
   spider_string *str,
-  key_range *start_key,
-  key_range *end_key,
+  const key_range *start_key,
+  const key_range *end_key,
   ulong sql_type,
   int link_idx
 ) {
@@ -14354,8 +14354,8 @@ int spider_mbase_handler::show_last_insert_id(
 }
 
 ha_rows spider_mbase_handler::explain_select(
-  key_range *start_key,
-  key_range *end_key,
+  const key_range *start_key,
+  const key_range *end_key,
   int link_idx
 ) {
   int error_num;