Long-awaited next commit for the next-generation tile system of Krita.
Took a long time to code it all in my spare time, despite the relative shortness of the patch.

It's rather evolutionary from the last mass-commit, in that the main change is a nice refactor of the shared tile data (I like it a lot better than it was before, even though it could still be better).

Has 2 (or 3) known issues at the moment:
* At program/testcase exit, the tile swapper will trigger an assertion. This is because I'm more assertive than before ;)
Basically, Krita seems to be leaking some memory, and the tile swapper wants all tiles to not leak at all (an example of a fix of such a leak was the recent work on the update strategies).
You can filter those pseudo-failing tests out by uncommenting the relevant asserts and deletes in KisTileSwapper::~KisTileSwapper

* Some KisFilterTests sometimes trigger another assert during program exectution. Will be investigated...

* While using my code to play with Krita, I sometimes seemed to get a random assert during painting or so, cause unknown (perhaps it even got fixed together with some other bugfix?)

I'm sure Boudewijn, Cyrille and even Pippin will love that it I'm committing this :-)
I guess they can celebrate it together with their fellow LGM'ers there in Wroclaw :-)