(Imported from
b53f8c187de8)
Author: Rusty Russell <rusty@rustorp.com.au>
Date: Thu Jun 10 13:27:51 2010 -0700
Since idtree assigns sequentially, it rarely reaches high numbers.
But such numbers can be forced with idr_get_new_above(), and that
reveals two bugs:
1) Crash in sub_remove() caused by pa array being too short.
2) Shift by more than 32 in _idr_find(), which is undefined, causing
the "outside the current tree" optimization to misfire and return NULL.