Added detection of memory overwrite with multi_malloc

This patch also fixes some bugs detected by valgrind after this
patch:

- Not enough copy_func elements was allocated by Create_tmp_table() which
  causes an memory overwrite in Create_tmp_table::add_fields()
  I added an ASSERT() to be able to detect this also without valgrind.
  The bug was that TMP_TABLE_PARAM::copy_fields was not correctly set
  when calling create_tmp_table().
- Aria::empty_bits is not allocated if there is no varchar/char/blob
  fields in the table.  Fixed code to take this into account.
  This cannot cause any issues as this is just a memory access
  into other Aria memory and the content of the memory would not be used.
- Aria::last_key_buff was not allocated big enough. This may have caused
  issues with rtrees and ma_extra(HA_EXTRA_REMEMBER_POS) as they
  would use the same memory area.
- Aria and MyISAM didn't take extended key parts into account, which
  caused problems when copying rec_per_key from engine to sql level.
- Mark asan builds with 'asan' in version strihng to detect these in
  not_valgrind_build.inc.
  This is needed to not have main.sp-no-valgrind fail with asan.

sql/sql_expression_cache.cc

@@ -114,7 +114,7 @@ void Expression_cache_tmptable::init()
 
   cache_table_param.init();
   /* dependent items and result */
-  cache_table_param.field_count= items.elements;
+  cache_table_param.field_count= cache_table_param.func_count= items.elements;
   /* postpone table creation to index description */
   cache_table_param.skip_create_table= 1;