test-revlog-raw: fix "genbits" implementation
The "genbits" implementation is actually incorrect. This patch fixes it. A
good "genbits" implementation should pass the below assertion:
n = 3 # or other number
l = list(genbits(n))
assert 2**(n*2) == len(set((l[i]<<n)+l[i+1] for i in range(len(l)-1)))
An assertion is added to make sure "genbits" won't work unexpectedly.
Greg Ward, author of the original bfiles extension
Na'Tosha Bard of Unity Technologies
Fog Creek Software
Special thanks to the University of Toronto and the UCOSP program