hugetlb: series to remove custom inode allocation

This series of patches removes the custom inode allocator from arch/i386/mm/hugetlbpage.c

It's broken up into 11 incremental steps that progressively reduce inode dependence, and in the final two stages replace the inode usage entirely with direct usage of radix trees and refcounting.

The level of testing is very low, but I'd like to release this early.

[1/11]  hugetlb: revert doublefreeing patch
[2/11]  hugetlb: wrap set_new_inode() with alloc_key()
[3/11]  hugetlb: wrap release path with release_key()
[4/11]  hugetlb: wrap hugetlb_prefault with prefault_key()
[5/11]  hugetlb: embed busy flag in key structure
[6/11]  hugetlb: remove direct usage of struct inode
[7/11]  hugetlb: substitute hugetlb_key for struct inode
[8/11]  hugetlb: reduce inode usage in prefault_key()
[9/11]  hugetlb: move inode attributes into hugetlb_key

[10/11] hugetlb: use radix trees instead of inodes [11/11] hugetlb: add reference counting to hugetlb_keys

Bill