Refactor *decay_time into *decay_ms.

Support millisecond resolution for decay times.  Among other use cases
this makes it possible to specify a short initial dirty-->muzzy decay
phase, followed by a longer muzzy-->clean decay phase.

This resolves #812.

include/jemalloc/internal/ctl.h

@@ -64,8 +64,8 @@ struct ctl_arena_s {
 	/* Basic stats, supported even if !config_stats. */
 	unsigned nthreads;
 	const char *dss;
-	ssize_t dirty_decay_time;
-	ssize_t muzzy_decay_time;
+	ssize_t dirty_decay_ms;
+	ssize_t muzzy_decay_ms;
 	size_t pactive;
 	size_t pdirty;
 	size_t pmuzzy;