[Sheepdog] expected bit size of __ffs

[Steven Dake]

Is __ffs expecting 64 bit parameters?  At line 18 of bitops.h, there is
a >> by 32, which with a 32 bit parameter results in the value 0.

unsigned long on 64 bit platforms = 64 bits, on 32 bit platforms, 32
bits.  A better solution to dealing with this long term is to use
stdint.h ie:

uint64_t 
uint32_t

I know there is no current support for 32 bit platforms, but proper
inttyping is always helpful.  This is one area C is suboptimal by
default. :)