A rollup of Bill's 11-patch series which replaces hugetlb's custom
inode with a bare radix tree.  Reviewed and acked by Rohit.

- revert doublefreeing patch

- Put set_new_inode() and the inode allocation loop into an
  alloc_key(), and introduce a new opaque type "struct hugetlb_key".

- Wrap the release path in alloc_shared_hugetlb_pages() with a
  release_key() function that handles the release.

- Wrap hugetlb_prefault() with prefault_key() in order to isolate the
  dependency on inodes for prefaulting the hugetlb vma.

- Replaces the usage of inode->i_writecount as a flag marking keys
  busy with a boolean flag field in struct htlbpagekey, and removes the
  last dependency of alloc_shared_hugetlb_pages() on struct inode.

- Remove the last direct usage of struct inode within the hugetlb
  functions.

- Removes many direct usages of struct inode within the key
  manipulation API in exchange for passing references to the key
  structure itself.

- Expand out prefault_key() into its hugetlb_prefault() component,
  but substitute stubs to abstract out inode access.

- Move uid/gid/mode/size fields used in struct inode and the checks
  on them into key management code and structures.

- Substitute direct usage of radix trees for inodes, and removes the
  custom-allocated inodes.

- Wrap up the release path by adding proper refcounting of keys.