wireproto: port branchmap to wire protocol v2 Differential Revision: https://phab.mercurial-scm.org/D3182

wireproto: port listkeys commands to wire protocol v2 Differential Revision: https://phab.mercurial-scm.org/D3181

wireproto: port keep command to wire protocol v2 This is pretty straightforward. Differential Revision: https://phab.mercurial-scm.org/D3180

wireproto: port heads command to wire protocol v2 After much thought and consideration, wire protocol version 2's commands will be defined in different functions from the existing commands. This will make it easier to implement these commands because it won't require shoehorning things like response formatting and argument declaration into the same APIs. For example, wire protocol version 1 requires that commands declare a fixed and ordered list of argument names. It isn't really possible to insert new arguments or have optional arguments without breaking backwards compatibility. Wire protocol version 2, however, uses CBOR maps for passing arguments. So arguments a) can be optional b) can be added without BC c) can be strongly typed. This commit starts our trek towards reimplementing the wire protocol for version 2 with the heads command. It is pretty similar to the existing heads command. One added feature is it can be told to operate on only public phase changesets. This is useful for making discovery faster when a repo has tens of thousands of draft phase heads (such as Mozilla's "try" repository). The HTTPv2 server-side protocol has had its `getargs()` implementation updated to reflect that arguments are a map and not a list. Differential Revision: https://phab.mercurial-scm.org/D3179

largefiles: wrap heads command handler more directly extensions.wrapfunction() is a more robust method for wrapping a function, since it allows multiple wrappers. While we're here, wrap the function registered with the command instead of installing a new command handler. Differential Revision: https://phab.mercurial-scm.org/D3178

wireproto: crude support for version 2 HTTP peer As part of implementing the server-side bits of the wire protocol command handlers for version 2, we want a way to easily test those commands. Currently, we use the "httprequest" action of `hg debugwireproto`. But this requires explicitly specifying the HTTP request headers, low-level frame details, and the data structure to encode with CBOR. That's a lot of boilerplate and a lot of it can change as the wire protocol evolves. `hg debugwireproto` has a mechanism to issue commands via the peer interface. That is *much* easier to use and we prefer to test with that going forward. This commit implements enough parts of the peer API to send basic requests via the HTTP version 2 transport. The peer code is super hacky. Again, the goal is to facilitate server testing, not robustly implement a client. The client code will receive love at a later time. Differential Revision: https://phab.mercurial-scm.org/D3177