worker: explain why pickle reading stream has to be unbuffered

bundle: quick fix to ludicrous performance penalty We tried a `hg bundle --base ':(tip^)' --rev 'all()'` on a large repository and it spent 3 minutes on this 2 list comprehensions. This change remove this cost. There are still a lot of low hanging fruits as the command still take 30 seconds. However this is a trivial patch with a massive speedup so I'll just sent it.

deltas: add a debug-delta-find command to analyse delta search See command documentation for details. For some reason, pytype is confused by our usage of None/deltainfo variable, so I had to quiet it.

deltas: add a `debug.revlog.debug-delta` config option enable output This provide a way to enable the code introduced in the previous changeset. This will provide a large amount of output when applying a bundle with details about each delta "computation".

deltas: add code to display information about the result of `finddeltainfo` I have been looking into performance issue around pull and getting more information about the computation and time involved into applying each revision is very useful. There will be various way to use this new output, so I am introducing the code first.

test: update `test-sparse-revlog` output This got changed at some point.

branching: fix wrong merge conflict resolution from 13dfad0f9f7a 13dfad0f9f7a merged stable into default, but accidentally added the _blockingreader class from stable (but deindented) instead of merging the changes from stable (2fe4efaa59af) into the existing _blockingreader class. This resulted in the _blockingreader being there two times.

debugdeltachain: detect a special case where parents are "skipped" See inline comment for details, this is a case where the delta is neither against p1 or p2, Yet it is still a simple delta part of a simple chain. We now display them as `skip1/skip2` instead of `other`.

debugdeltachain: document the possible value for deltatype So that one can understand what is displayed by the command.

debugdeltachain: also display p1/p2 Looking at the parents is a common need when trying to understanding why a delta was chosen, having it readily available helps a lot.

debugdeltachain: glob variance of "test-generaldelta" We mostly care about generaldelta happening, the exact details of storage size variation is not really important so we can glob it instead of having multiple lines for each variances. This will make updating the output of the command simpler.

debugdeltachain: use the symbolic constant to access entry information This is more robust and easier to read