Cache loaded arguments

Arguments loaded on pages created by PageManager in function pm_arg_load() multiple times. It called by _menu_translate() function (_menu_translate() -> _menu_load_objects() -> call_user_func_array() -> pm_arg_load()), and _menu_translate() is called multiple times with the same arguments.

First time it loadings at bootstrap from menu_get_item() when system detect current menu router (menu_get_item() -> _menu_translate()).
Second time in template_preprocess_page() when build tabs (template_preprocess_page() -> menu_local_actions() -> menu_local_tasks() -> _menu_translate()).
And another case, someone can use it directly to get loaded context.

Next, every time pm_arg_load() is calling it builds full context with full content renderable array with all elements and forms, and load all needed entities. And It can take a long time if form is big and have field_collections, entities and inner forms. In my case building context takes 2 seconds (a lot of entity references, a lot of field_collections, which have own entity references and own inner field_collections, which ... etc). So it's reasonable to build it one times only, but it build second time when trying access to all tabs. One more: it make full build context of my heavy form for checking access to tabs only!

I dont think that is ctools (or page_manager) module's fault. Need to optimize _menu_translate(), but we can smooth this bug by applaying cache loaded arguments. It seems that it unnecessarily to build context more then 1 time, so at second loading we can return context builded before, so we can use static cache. Unlikely access rights would change during building page.

I created patch, which add cache for loaded arguments and my pages are loading two times faster!

P.S. I know, my English not so good. =)