Disable interval-based profile dumps by default.

It is common to have to specify something like JEMALLOC_OPTIONS=F31i,
because interval-based dumps are often unuseful or too expensive.
Therefore, disable interval-based dumps by default.  To get the previous
default behavior it is now necessary to specify 31I as part of the
options.

jemalloc/include/jemalloc/internal/prof.h

@@ -11,7 +11,7 @@ typedef struct prof_s prof_t;
 /* Option defaults. */
 #define	LG_PROF_BT_MAX_DEFAULT		2
 #define	LG_PROF_SAMPLE_DEFAULT		0
-#define	LG_PROF_INTERVAL_DEFAULT	30
+#define	LG_PROF_INTERVAL_DEFAULT	-1
 
 /*
  * Hard limit on stack backtrace depth.  Note that the version of