revset: avoid returning duplicates when returning ancestors Before this patch, _revancestors were giving false result when a revision was duplicated in the input. Duplicated entry are rare but may happen when using the `%lx` notation internally. This series has no visible impact on the performance of the function according to benchmark.

revset: use an iterator instead of a dequeue in ancestors() The dequeue was actually just used to be able to pop value one at a time. Building the dequeue means we are reading all the input value at once at the beginning of the evaluation. This defeat the lazyness of revset. We replace the deque with iterator usage for the sake of simplicity and lazyness. This provide massive speedup to get the first result if the input set is big max(::all()) before) wall 0.001917 comb 0.000000 user 0.000000 sys 0.000000 (best of 1115) after) wall 0.000107 comb 0.000000 user 0.000000 sys 0.000000 (best of 22222)

revset: return early when revs is empty By introducing an early return in _revancestors() when revs is empty, we make it so inputrev is never None, which simplifies the subsequent code.

revset: rename 'revsnode' to 'inputrev' in ancestors We usually use 'node' for variable containing 20 bytes hash. There is nothing nodish in this variable, so we rename it to "inputrev" as it old the next entry of the iteration.