admin BitFieldListFilter not working as expected

[bendavis78]

BitFieldListFilter seems to filter based on "exact", as opposed to a bitwise operation. So when you select the third item (mask=4), you essentially get this:

queryset.filter(flags=4)

Which will not return the desired result. The queryset() method should be overridden in order to perform the correct bitwise operation when filtering.

[mateuszmandera]

@ortholeviator What should be the status of this issue following #106?