Remove fields by module

Here's a patch then. This patch does the following:

1) adds a 'module' column to each of the views tables and adds an update to the install file

2) alters the code in _views_get_tables() and _views_get_arguments() to store the module name in the cached arrays

3) alters the code that saves the views fields so it saves the module name in the table

4) creates a new helper function called views_get_module_fields($module) to return an array of all of that modules fields that are currently used in views

5) creates a new helper function called views_delete_module_fields($module, $field_name = NULL) that deletes all the module fields from views tables

6) creates a new helper function called views_save_all() that pulls up and saves all views so their tables get updated.

Oops, some debugging cruft was left in that last patch.

I've been working a bit more with this patch and have been struggling with some views that kept trying to use deleted fields even after I cleared all the caches and removed the fields from all the views tables. After going down a dozen blind allies, I think I am figuring some of it out.

Part of the problem was of my own creation since I was caching some views info in my own caches instead of the views cache so views_invalidate_cache() wasn't clearing them and my bad cached values were getting re-inserted. I'm doing some patching of my modules now to move anything I cache that has any views info to the views cache so it will get cleared whenever views_invalidate_cache() is called.

Another thing that may be a problem is the static variables in _views_get_tables() and _views_get_arguments(). I think old values might be getting saved in the static values and then getting reinserted into the view when they shouldn't. I'm playing around with adding a $reset flag to clear those static values out when views_invalidate_cache() is called so no old values leak back in. I'm still trying to be sure whether this is really needed.

One last static value that might or might not be a problem is a static value in _views_load_view(). I'm wondering if that might be another place where invalid info is getting trapped and reinserted.

It makes sense to go ahead and add a hook here. Actually I can maybe see two hooks -- one for anytime a view is edited and one for anytime views_invalidate_cache() is called (when presumably all other modules that rely on Views data need to flush their own values).

I can try to work that in, too.