Corruption on pasting nested tuplet

Ubuntu 14.04, GIT commit: e96036e

1) load attached score (contains half note triplet, with nested quarter note triplet on last note)
2) select the quarter note triplet
3) copy
4) click measure rest in next measure
5) paste

Result: corruption

We shouldn't be allowing this copy in the first place, as we are not actually copying a complete tuplet. Apparently, the code that detects this is being fooled in that we are copying a complete inner tuplet.

I plan to incorporate a fix for this into my outstanding PR to fix other corruptions on tuplet copy. The commits will be separate so we easily incldue just one fix if we wish. But my plan is to be running a build with these fixes from now on, and to periodically test different aspects of tuplet copying, to see if there are regressions. As it is, my previous fix doens't solve this particular corruption, but it does somehow make it less extreme - instead of a whole note, we get a quarter note. But the rests are still present, because at a basic level, we just can't support this kind of paste.