docker-pytype: use version v2.1 of the CI image It use a more recent pytype as far as I understand.

context: some gratuitous documentation improvement I wrote it as I was reading the code.

profiling: add a py-spy profiling backend The recommended way to use this backend is by setting the config `profiling.output` to point to a file because py-spy output is not human-readable.

copytracing: fix a bug in an edge case in metadata.compute_all_files_changes

rhg: ignore readonly FS error when saving dirstate The error is already ignored when the .hg directory is read-only, so this is only fair. (the python hg is silent on readonly fs, too)

commit: set whole manifest entries at once (node with its associated flags) Add a new function manifest.set that sets whole manifest entries at once, so the caller doesn't have to do two separate operations: m[p] = n m.set_flags(f) becomes: m.set(p, n, f) This obviously saves an extra lookup by path, and it also lets the underlying manifest implementation to be more efficient as it doesn't have to deal with partially-specified entries. It makes the interaction conceptually simpler, as well, since we don't have to go through an intermediate state of incorrect partially-written entry. (the real motivation for this change is an alternative manifest implementation where we batch pending writes, and dealing with fully defined entries makes the batching logic muchsimpler while avoiding slowdown due to alternating writes and reads)