Add junk/zero filling unit tests, and fix discovered bugs.

Fix growing large reallocation to junk fill new space.

Fix huge deallocation to junk fill when munmap is disabled.

test/unit/zero.c

@@ -0,0 +1,78 @@
+#include "test/jemalloc_test.h"
+
+#ifdef JEMALLOC_FILL
+const char *malloc_conf =
+    "abort:false,junk:false,zero:true,redzone:false,quarantine:0";
+#endif
+
+static void
+test_zero(size_t sz_min, size_t sz_max)
+{
+	char *s;
+	size_t sz_prev, sz, i;
+
+	sz_prev = 0;
+	s = (char *)mallocx(sz_min, 0);
+	assert_ptr_not_null((void *)s, "Unexpected mallocx() failure");
+
+	for (sz = sallocx(s, 0); sz <= sz_max;
+	    sz_prev = sz, sz = sallocx(s, 0)) {
+		if (sz_prev > 0) {
+			assert_c_eq(s[0], 'a',
+			    "Previously allocated byte %zu/%zu is corrupted",
+			    0, sz_prev);
+			assert_c_eq(s[sz_prev-1], 'a',
+			    "Previously allocated byte %zu/%zu is corrupted",
+			    sz_prev-1, sz_prev);
+		}
+
+		for (i = sz_prev; i < sz; i++) {
+			assert_c_eq(s[i], 0x0,
+			    "Newly allocated byte %zu/%zu isn't zero-filled",
+			    i, sz);
+			s[i] = 'a';
+		}
+
+		if (xallocx(s, sz+1, 0, 0) == sz) {
+			s = (char *)rallocx(s, sz+1, 0);
+			assert_ptr_not_null((void *)s,
+			    "Unexpected rallocx() failure");
+		}
+	}
+
+	dallocx(s, 0);
+}
+
+TEST_BEGIN(test_zero_small)
+{
+
+	test_skip_if(!config_fill);
+	test_zero(1, SMALL_MAXCLASS-1);
+}
+TEST_END
+
+TEST_BEGIN(test_zero_large)
+{
+
+	test_skip_if(!config_fill);
+	test_zero(SMALL_MAXCLASS+1, arena_maxclass);
+}
+TEST_END
+
+TEST_BEGIN(test_zero_huge)
+{
+
+	test_skip_if(!config_fill);
+	test_zero(arena_maxclass+1, chunksize*2);
+}
+TEST_END
+
+int
+main(void)
+{
+
+	return (test(
+	    test_zero_small,
+	    test_zero_large,
+	    test_zero_huge));
+}