manifestmerge: handle abort on local unknown, remote created files This replaces the _checkunknown call in calculateupdates with a more performant version. On a repository with over 150,000 files, this speeds up an update by 0.6-0.8 seconds, which is up to 25%. This does not introduce any UI changes. There is existing test coverage for every case, mostly in test-merge*.t.

manifestmerge: pass in branchmerge and force separately This will be used in an upcoming patch.

manifest: use a size 3 LRU cache to store parsed manifests Previously, the manifest cache would store the last manifest parsed. We could run into situations with operations like update where we would try parsing the manifest for a revision r1, then r2, then r1 again. This increases the cache size to 3 to avoid that bit of performance fragility.