changegroup: the node list might be an empty generator (fix
issue1678)
store encoding: .i/.d encoding for non-store repo (broken by
810387f59696)
replace "i in range(len(xs))" with "i, x in enumerate(xs)"
The remaining occurrences should be the ones where "xs" is mutated or
where "i" is used for index arithmetic.
util: simplify range expression
The n index variable was unused. Every iteration would pop one element
off of parts, so the for loop can be replaced with a while loop.