- fix for bug when creating bitmaps

- fix for bug seen when running test "type_datetime" with Maria
(wrong data_file_length in maria_repair())
- fix for bug seen when running test "repair" with Maria
(myisam_sort_buffer_size was influencing Maria)


sql/handler.cc:
  Sounds illogical to store myisam_sort_buffer_size into a structure
  used by all engines. There are only MyISAM and Maria which used 
  sort_buffer_size: they can get their value from their respective
  system variable (myisam|maria_sort_buffer_size). Using MyISAM's value
  for all engines was wrong (myisam_sort_buffer_size influenced Maria).
sql/handler.h:
  not needed
storage/maria/ha_maria.cc:
  check_opt->sort_buffer_size was myisam_sort_buffer_size; Maria
  must use maria_sort_buffer_size instead.
storage/maria/ma_bitmap.c:
  don't use my_chsize() now that Monty re-explained the problem to me :)
storage/maria/ma_check.c:
  making maria_repair() work like maria_repair_by_sort(): sort_param.filepos
  must be set at start then possibly corrected by create_new_data_handle();
  in the opposite order, filepos is finally set to 0, and if the table
  has no records, it stays 0 and this causes state.data_file_length
  to be 0 which is incorrect for a BLOCK_RECORD table having always
  at least one bitmap page.
storage/maria/ma_pagecache.c:
  Comments
storage/myisam/ha_myisam.cc:
  check_opt->sort_buffer_size is gone

sql/handler.h

@@ -890,7 +890,6 @@ typedef class Item COND;
 typedef struct st_ha_check_opt
 {
   st_ha_check_opt() {}                        /* Remove gcc warning */
-  ulong sort_buffer_size;
   uint flags;       /* isam layer flags (e.g. for myisamchk) */
   uint sql_flags;   /* sql layer flags - for something myisamchk cannot do */
   KEY_CACHE *key_cache; /* new key cache when changing key cache */