Numerous LVM fixes & cleanups.
Gets things compiling again, and allegedly works according to feedback.
Mostly from Anders in absence of any maintainence by LVM people.

There are two critical problems with lvm in 2.5.2-pre11 (and earlier).
* ioctls on the chardev allocates a >4k lv_t on stack. if the ioctl is
LV_CREATE, LV_EXTEND, LV_REDUCE or LV_RENAME data is copied into this
and the task_struct will most certainly be corrupted.
* sizeof(lv_t) differs between user and kernelspace. The userspace version
of the lv_t structure is much smaller than the kernelspace version. This
leads to corruption of memory in the userspace application when an lv_t is
copied from kernelspace to userspace, as in "vgdisplay -v"

The following patch addresses these two issues. It puts the user-space
version of the lv_t into a substructure of the kernelspace version. When
communicating to userspace just the userlv_t part is used. This avoids the
allocation of the lv_t on the stack by allocation just a userlv_t instead.