branches/zip: fix compiler warning

Change the definition of add_on from ulint to ullint, to eliminate
the warning in .\btr\btr0cur.c:
conversion from 'ullint' to 'ulint', possible loss of data

Approved by:	Heikki (on IM)

btr/btr0cur.c

@@ -3164,7 +3164,7 @@ btr_estimate_number_of_different_key_vals(
 	ulint		total_external_size = 0;
 	ulint		i;
 	ulint		j;
-	ulint		add_on;
+	ullint		add_on;
 	mtr_t		mtr;
 	mem_heap_t*	heap		= NULL;
 	ulint		offsets_rec_[REC_OFFS_NORMAL_SIZE];