Bug when filtering child/parent items

[Nicklas Nordborg]

The possibility to filter on parent/child items in table listing was added in #1129.

While the equality operator works fine, the inequality operator can give "confusing" results when an item has more than one child, since it matches on each child item individually and not on all children as a whole.

Consider the following setup with parent/child items:

Parent	Child
A	A.1, A.2, A.3
B	B.1, B.2
C	C.1
D	D.2
E	E.3

Now test the following filters:

Filter	Result
=%.1	A, B, C
<>%.1	A, B, D, E

The first result is expected, but not the second, which matches A and B because they have other child items.

The current implementation for '<>' can't be easily defined by any existing "set operations" (eg. contains/not contains). The most intuitive approach would be if '=' can be sort of equivalent to 'contains' and '<>' to be equivalent to 'not contains'. Eg. the second filter above should return only D and E.

The simple case described above should be fairly stright-forward, but we also need to think about list-filters:

Filter	Result
=%.1|%.2	A, B, C, D
<>%.1|%.2	A, E

Again, the first is ok, but the second should only return E.

[Nicklas Nordborg]

(In [6205]) Fixes #1736: Bug when filtering child/parent items