Make the loop support stuff be much less evil, and make it cope

Make the loop support stuff be much less evil, and make it cope
with 2.6.x asm/posix_types.h, which has done singularly evil thing
by yanking __kernel_dev_t and renaming it.  The loop interface was
really poorly designed in the first place.  The new 64 bit loop
interface looks to be somewhat less horrible, too bad it is only
present in 2.6.x kernels.
 -Erik