manifest: fix some pure-Python parser bits to work on Python 3

tests: make test-manifest finish importing in Python 3 The test is still broken, but now it executes.

tests: drop assertIn polyfill now that we're 2.7-only

perf: benchmark command for revlog indexes We didn't have explicit microbenchmark coverage for loading revlog indexes. That seems like a useful thing to have, so let's add it. We currently measure the low-level nodemap APIs. There is room to hook in at the actual revlog layer. This could be done as a follow-up. The hackiest thing about this patch is specifying revlog paths. Other commands have arguments that allow resolution of changelog, manifest, and filelog. I needed to hook in at a lower level of the revlog API than what the existing helper functions to resolve revlogs allowed. I was too lazy to write some new APIs. This could be done as a follow-up easily enough. Example output for `hg perfrevlogindex 00changelog.i` on my Firefox repo (404418 revisions): ! revlog constructor ! wall 0.003106 comb 0.000000 user 0.000000 sys 0.000000 (best of 912) ! read ! wall 0.003077 comb 0.000000 user 0.000000 sys 0.000000 (best of 924) ! create index object ! wall 0.000000 comb 0.000000 user 0.000000 sys 0.000000 (best of 1803994) ! retrieve index entry for rev 0 ! wall 0.000193 comb 0.000000 user 0.000000 sys 0.000000 (best of 14037) ! look up missing node ! wall 0.003313 comb 0.000000 user 0.000000 sys 0.000000 (best of 865) ! look up node at rev 0 ! wall 0.003295 comb 0.010000 user 0.010000 sys 0.000000 (best of 858) ! look up node at 1/4 len ! wall 0.002598 comb 0.010000 user 0.010000 sys 0.000000 (best of 1103) ! look up node at 1/2 len ! wall 0.001909 comb 0.000000 user 0.000000 sys 0.000000 (best of 1507) ! look up node at 3/4 len ! wall 0.001213 comb 0.000000 user 0.000000 sys 0.000000 (best of 2275) ! look up node at tip ! wall 0.000453 comb 0.000000 user 0.000000 sys 0.000000 (best of 5697) ! look up all nodes (forward) ! wall 0.094615 comb 0.100000 user 0.100000 sys 0.000000 (best of 100) ! look up all nodes (reverse) ! wall 0.045889 comb 0.050000 user 0.050000 sys 0.000000 (best of 100) ! retrieve all index entries (forward) ! wall 0.078398 comb 0.080000 user 0.060000 sys 0.020000 (best of 100) ! retrieve all index entries (reverse) ! wall 0.079376 comb 0.080000 user 0.070000 sys 0.010000 (best of 100)