Remove pre-2.6.32 compatibility code (WIP)

Over the years the SPL code bases has accumulated compatibly code to allow it to continue to build against a wide range of Linux kernels.  In general this is desirable because it makes the code flexible.  However, once support for these old kernels is no longer need and is not being actively tested it should be removed.  This helps keep the code simple and understandable.

The spl-0.6.x releases have supported kernels all the way back to 2.6.26.  This patch stack moves that cut off up to 2.6.32 and newer kernels.  This ensures we still support all the major enterprise distributions which are largely locked in to 2.6.32 based kernels.  And at the same time we're able to shed a large amount of compatibility code which simplifies maintenance and new development.

While this patch stack looks large it's not as daunting as it might initially appear.  The vast majority of patches simply remove configure checks and the associated deadcode.  Several of the changes do need to slight rework functions but this has been kept to a minimum.