[MERGE] BTreeIndex intern()

[Michael Hudson]

John Arbash Meinel wrote:

> - From what I can tell, I think we have a small memory leak somewhere,
> because the current 'WorkingSize' doesn't match the size of objects I
> can access using PyMemoryDump. I feel like it is something introduced
> recently, but I haven't found a great way to actually debug it yet.

valgrind is pretty good at this, I think...

Cheers,
mwh