KRecursiveFilterProxyModel: The model was not working properly

[Impact]
KRecursiveFilterProxyModel fails to display items in various treemodel scenarios. More technical details to be found at https://git.reviewboard.kde.org/r/120119/

[Test Case]
* use every filter in KMail. Items should not be missing
* create Kate projects and filter them in the projectview.

[Regression Potential]
Unlikely approved upstream, unit tested, adopted in Fedora already. Regressions would likely appear as filtering things that shouldn't be filtered in: kate, kmail, (akonadi?) imap subscription, knotes' config dialog, various akonadi GUIs.

[Other Info]
N/A

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Hi,

This patch should be included as it fixes a critical bug in kdelibs which renders Kontact unable to show user data. The data is actually there, but not visible or accessible to the user, and therefore is often perceived as a data loss issue.

The patch itself is small (-11/+5 lines), contained entirely in private code in the affected library, and comes with a unit test to ensure quality.

There is a approved upstream review request to include:

        https://git.reviewboard.kde.org/r/120119/

The bug it fixes continues to affect users.

So despite waiting for upstream response, it is already being packaged in Fedora packages as well as being shipped to large institutional users (at least one of which uses a Debian OS as the desktop client) by downstream
companies such as Kolab Systems. At debian it got into jessie http://bugs.debian.org/775114

By including this well-tested and already deployed patch, Ubuntu can ensure that users relying on Kontact working well (among other KDE applications which use this same functionality) will not need to go elsewhere (e.g. another downstream) for a patched version of the kdelibs package.

Regads,

sandro