Bug #12796: Record lost in HEAP table

Two handler objects were present, one was used for an insert and the other for a select
The state of the statistics was local to the handler object and thus the other handler
object didn't notice the insert.
Fix included:
1) Add a new variable key_stat_version added to whenever statistics was considered in need
of update (previously key_stats_ok= FALSE in those places)
2) Add a new handler variable key_stat_version assigned whenever key_stats_ok= TRUE was set
previously
3) Fix records_in_range to return records if records <= 1
4) Fix records_in_range to add 2 to rec_per_key to ensure we don't specify 0 or 1 when it isn't
and thus invoking incorrect optimisations.
5) Fix unique key handling for HEAP table in records_in_range

heap/hp_create.c

@@ -104,6 +104,7 @@ int heap_create(const char *name, uint keys, HP_KEYDEF *keydef,
       DBUG_RETURN(1);
     }
     share->keydef= (HP_KEYDEF*) (share + 1);
+    share->key_stat_version= 1;
     keyseg= (HA_KEYSEG*) (share->keydef + keys);
     init_block(&share->block, reclength + 1, min_records, max_records);
 	/* Fix keys */