tests: mock getpid to reduce glob usage Updating tests based on ac49ecb2a897.

changegroup: drop special-casing of flat manifests Since c08814b48ae5 (changegroup: avoid iterating the whole manifest, 2015-12-04), the manifest linkrev callback iterates over only the files that were touched according the the changeset. Before that change, we iterated over all files returned in manifest.readfast(). That method returns the files in the delta, if the delta parent is a parent, otherwise it returns the full manifest. Most manifest revisions end up using one of the parents as its delta parent, so most of the time, the method returns a short manifest. It seems that that happens often enough that it doesn't really matter; I could not reproduce the timings reported in that change. Since the treemanifest code now works quite differently, and since that code also works correctly for flat manifests, let's drop the special-casing of flat manifests.

changegroup: fix treemanifests on merges The current code for generating treemanifest revisions takes the list of files in the changeset and finds the directories from them. This does not work for merges, since a merge may pick file A from one side and file B from another and neither of them would appear in the changeset's "files" list, but the manifest would still change. Fix this by instead walking the root manifest log for all needed revisions, storing all needed file and subdirectory revisions, then recursively visiting the subdirectories. This also turns out to be faster: cloning a version of hg core converted to treemanifests went from ~28s to ~19s (timing somewhat unfair: before this patch, timed until crash; after this patch, timed until manifests complete). The new algorithm is used only on treemanifest repos. Although it works equally well on flat manifests, we leave the iteration over files in the changeset for flat manifests for now.