Implement chunk hook support for page run commit/decommit.

Cascade from decommit to purge when purging unused dirty pages, so that
it is possible to decommit cleaned memory rather than just purging.  For
non-Windows debug builds, decommit runs rather than purging them, since
this causes access of deallocated runs to segfault.

This resolves #251.

src/chunk_dss.c

@@ -67,7 +67,7 @@ chunk_dss_prec_set(dss_prec_t dss_prec)
 
 void *
 chunk_alloc_dss(arena_t *arena, void *new_addr, size_t size, size_t alignment,
-    bool *zero)
+    bool *zero, bool *commit)
 {
 	void *ret;
 
@@ -137,13 +137,15 @@ chunk_alloc_dss(arena_t *arena, void *new_addr, size_t size, size_t alignment,
 					chunk_hooks_t chunk_hooks =
 					    CHUNK_HOOKS_INITIALIZER;
 					chunk_dalloc_wrapper(arena,
-					    &chunk_hooks, cpad, cpad_size);
+					    &chunk_hooks, cpad, cpad_size,
+					    true);
 				}
 				if (*zero) {
 					JEMALLOC_VALGRIND_MAKE_MEM_UNDEFINED(
 					    ret, size);
 					memset(ret, 0, size);
 				}
+				*commit = true;
 				return (ret);
 			}
 		} while (dss_prev != (void *)-1);