Integrate whole chunks into unused dirty page purging machinery.

Extend per arena unused dirty page purging to manage unused dirty chunks
in aaddtion to unused dirty runs.  Rather than immediately unmapping
deallocated chunks (or purging them in the --disable-munmap case), store
them in a separate set of trees, chunks_[sz]ad_dirty.  Preferrentially
allocate dirty chunks.  When excessive unused dirty pages accumulate,
purge runs and chunks in ingegrated LRU order (and unmap chunks in the
--enable-munmap case).

Refactor extent_node_t to provide accessor functions.

include/jemalloc/internal/jemalloc_internal.h.in

@@ -368,8 +368,13 @@ typedef unsigned index_t;
 #include "jemalloc/internal/mutex.h"
 #include "jemalloc/internal/mb.h"
 #include "jemalloc/internal/bitmap.h"
-#include "jemalloc/internal/extent.h"
+#define	JEMALLOC_ARENA_STRUCTS_A
 #include "jemalloc/internal/arena.h"
+#undef JEMALLOC_ARENA_STRUCTS_A
+#include "jemalloc/internal/extent.h"
+#define	JEMALLOC_ARENA_STRUCTS_B
+#include "jemalloc/internal/arena.h"
+#undef JEMALLOC_ARENA_STRUCTS_B
 #include "jemalloc/internal/base.h"
 #include "jemalloc/internal/rtree.h"
 #include "jemalloc/internal/chunk.h"
@@ -933,7 +938,8 @@ ivsalloc(const void *ptr, bool demote)
 	if (node == NULL)
 		return (0);
 	/* Only arena chunks should be looked up via interior pointers. */
-	assert(node->addr == ptr || node->size == 0);
+	assert(extent_node_addr_get(node) == ptr ||
+	    extent_node_achunk_get(node));
 
 	return (isalloc(ptr, demote));
 }