forces block cache to be enabled with a node_access module present and keys the cache entries by the $_SERVER['HTTP_HOST']

force_blockcache.patch

diff U modules/block/block.module block/block.module
--- modules/block/block.module	Mon Jan 19 22:26:36 1970
+++ modules/block/block.module	Mon Jan 19 22:26:36 1970
@@ -515,4 +515 @@
-          // Try fetching the block from cache. Block caching is not compatible with
-          // node_access modules. We also preserve the submission of forms in blocks,
-          // by fetching from cache only if the request method is 'GET'.
-          if (!count(module_implements('node_grants')) && $_SERVER['REQUEST_METHOD'] == 'GET' && ($cid = _block_get_cache_id($block)) && ($cache = cache_get($cid, 'cache_block'))) {
+          if ($_SERVER['REQUEST_METHOD'] == 'GET' && ($cid = _block_get_cache_id($block)) && ($cache = cache_get($cid, 'cache_block'))) {
@@ -576,0 +574 @@
+    $cid_parts[] = $_SERVER["HTTP_HOST"];
diff U modules/system/system.admin.inc system/system.admin.inc
--- modules/system/system.admin.inc	Mon Jan 19 22:26:36 1970
+++ modules/system/system.admin.inc	Mon Jan 19 22:26:36 1970
@@ -1336,2 +1336,2 @@
-    '#disabled' => count(module_implements('node_grants')),
-    '#description' => t('Note that block caching is inactive when modules defining content access restrictions are enabled.'),
+//    '#disabled' => count(module_implements('node_grants')),
+//    '#description' => t('Note that block caching is inactive when modules defining content access restrictions are enabled.'),