WL#2126 - Multi_read_range.

Added the required structures and functions for
handing over multiple key ranges to the table handler.


include/my_base.h:
  WL#2126 - Multi_read_range.
  Moved key range flags from sql/opt_range.h to here.
  Added the multi-range structure.
sql/handler.cc:
  WL#2126 - Multi_read_range.
  Added the new table handler methods.
sql/handler.h:
  WL#2126 - Multi_read_range.
  Added a new table flag.
  Added a declaration for the handler buffer.
  Added new elements to class handler.
  Added new function declarations.
sql/mysqld.cc:
  WL#2126 - Multi_read_range.
  Added an option to set new system variable 'multi_range_count'.
sql/opt_range.cc:
  WL#2126 - Multi_read_range.
  Added initialization for the new class members.
  Added initialization for the extended get_next().
  Added de-initialization for the allocated buffers.
  Added a buffer allocation method.
  Added an inner loop to collect multiple ranges.
  Adapted range collection loops to the new initialization.
sql/opt_range.h:
  WL#2126 - Multi_read_range.
  Moved key range flags from here to include/my_base.h.
  Added new elements to class QUICK_RANGE_SELECT.
  Added a copy constructor.
sql/records.cc:
  WL#2126 - Multi_read_range.
  Added a call of the allocation method.
sql/set_var.cc:
  WL#2126 - Multi_read_range.
  Added the new system variable 'multi_range_count'.
sql/sql_class.h:
  WL#2126 - Multi_read_range.
  Added the new system variable 'multi_range_count'.

sql/sql_class.h

@@ -388,6 +388,7 @@ struct system_variables
   ulong max_sort_length;
   ulong max_tmp_tables;
   ulong max_insert_delayed_threads;
+  ulong multi_range_count;
   ulong myisam_repair_threads;
   ulong myisam_sort_buff_size;
   ulong net_buffer_length;