Make `in_bulk()` respect `no_dereference()`

The issue here is that the `in_bulk()` query set method does not honor `no_dereference()`, such that accessing attributes on items fetched in bulk always triggers a dereference, even if the programmer has asked for no dereferencing.

I'll write a test case if this looks like the way to fix this.

Possibly related to #372 and #517.