From: Jim Houston <jim.houston@comcast.net>

- Adds idr_get_new_above(), whihc permits us to do a first-fit search
  from a specified offset rather than always from zero.

- Add IDR_INIT() DEFINE_IDR() constructors.  Often idr's are singletons
  and having to cook up an initcall for them is a pain.

This is needed by the "Increase number of dynamic inodes in procfs" patch.