Extend Meta Tree on Free-Tree Extensions

[m-stein]

"Free-Tree Extension" requests are already handled properly by the CBE except that the meta tree isn't extended according to the new Free-Tree size so far. The Meta-Tree adaption is necessary because the Meta Tree must always have at least as many leaf nodes as the Free Tree and the Meta Tree have inner nodes. This ensures that Copy-On-Write on those inner nodes can always be done on-the-flight.