Disable the prefetch code in the InnoDB internal SQL parser.

This change is a followup to
vasil.dimov@oracle.com-20110907145810-v98kldmho23vhhic
which triggered the usage of the prefetch and valgrind tests spat lots of
warnings.

The prefetch code will be removed.

Discussed with:	Marko (over IM)

storage/innodb_plugin/row/row0sel.c

@@ -63,7 +63,13 @@ Created 12/19/1997 Heikki Tuuri
 
 /* Number of rows fetched, after which to start prefetching; MySQL interface
 has another parameter */
-#define SEL_PREFETCH_LIMIT	1
+/* The prefetch code in the internal SQL is disabled because it has probably
+never been used and has been found to contain a memory leak and a bug of
+accessing uninitialized memory. Some simple performance tests show that
+disabling it makes no difference in performance. It will be removed, but
+until the removal happens we disable it by setting SEL_PREFETCH_LIMIT to a
+high value. */
+#define SEL_PREFETCH_LIMIT	1000000000
 
 /* When a select has accessed about this many pages, it returns control back
 to que_run_threads: this is to allow canceling runaway queries */