push: restrict common discovery to the pushed set This changeset make use of the ability of the set discovery to only search common changeset for a subset of the repository. Restricting that search to the pushed set avoid potential waste of time finding out the status of many unrelated related revision. Repository with many heads were especially badly affected by this. Here is an example of findcommonhead discovery for pushing 11 outgoing changeset on a repository with tens of thousand of unrelated heads. (discovery run over a ssh link to localhost). Before: queries: 92 time: 44.1996s After: queries: 3 time: 0.6938s A x63 speedup even with a network link without latency.

setdiscover: allow to ignore part of the local graph Currently, the push discovery first determines the full set of common nodes before looking into what changesets are outgoing. When pushing a specific subset, this can lead to pathological situations where we search for the status of thousand of local heads that are unrelated to the requested pushes. To fix this, we need to teach the discovery to ignores part of the graph. Most of the necessary pieces were already in place. This changeset just makes them available to higher level API and tests them. Change actually impacting pushes are coming in a later changeset.

largefiles: allow to run 'debugupgraderepo' on repo with largefiles The extensions wrap the necessary function to ensure the 'largefiles' requirements won't be dropped. It is now possible to run `hg debugupgraderepo` on a repository with largefiles.

upgraderepo: allow extension to register preserved requirements Some requirement does not directly result from config and needs more advanced logic to be preserved. The current example is 'largefiles'. We add a hook point in the upgrade code so that extensions can handle these cases. The 'largefiles' extension will use it in the next changeset.