Support for cache invalidation on `bulk_update()` method

[ashwani99]

Currently, support for bulk_create() is present but not bulk_update(). Any thoughts on adding this?

Some inspiration can be taken from #136

[Suor]

.bulk_create() is already invalidated, you can look at the code in here. Unlike .bulk_update() it already had all changed objects with all their fields, do it doesn't require extra database queries to invalidate.

[pg1671]

Hi @Suor .. not sure why this was closed? It doesn't indicate the problem was resolved.

I have started to use bulk_update and realised the updates were not invalidated in the cache leading to strange behaviour in the application.

Is it best not to use bulk_update when using django-cacheops?

[Suor]

Not sure why I closed this. There might be no efficient way to handle this though, requires some investigation.