device-mapper v4 ioctl interface patchset

[Joe Thornber]

Linus,

Please merge.

These 2 patches implement the new ioctl interface for device-mapper.
This new interface is selectable with a config option, people can
continue to use the v1 interface if they wish.

The main issues that v4 addresses are:

i)  ioctl structure size issues on different architectures.

ii) tables can now be preloaded to avoid having to allocate memory
    while devices are suspended.

iii) Fix a userland race condition associated with the 'wait for
     event' ioctl.

- Joe