bundle2: convey PushkeyFailed error over the wire We add a way to convey the precise exception. This will allow better error message on the server.

bundle2: also capture reply capability on failure When unbundling over the wire is aborted, we have a mechanism to convey the error inside a bundle part. As we add support for more errors, we need to know if the client will support them. For this purpose, we duck punch the reply capabilities of the client on the raised extensions. This is similar to what is done to salvage the server output on error.

bundle2: add an 'error' capability This capability will be extended as new error type is introduced.

merge with stable

templater: introduce indent function

hgewb: disable progress when serving (issue4582) Before this patch, progress bar could be displayed when serving, creating hypothetical problems.

test-subrepo-recursion.t: fix progress output on no-hardlink systems

test-ssh: stablize for platform-specific shell quoting Windows and OpenVMS use double quotes instead of single.

push: catch and process PushkeyFailed error We add a way to register "pushkey failure callback" that will be used if the push is aborted by a pushkey failure. A part generator adding mandatory pushkey parts should register a failure callback for all of them. The callback will be in charge of generating a meaningful abort if this part fails. If no callback is registered, the error is propagated. Catch PushkeyFailed error in exchange.

bundle2: introduce a PushkeyFail error to abort unbundle on pushkey error The pushkey code is generic and the server side has little context on what the client is trying to achieve. Generating interesting error messages server side would be challenging. Instead we introduce a dedicated exception that carries more data. In particular, it carries the id of the part which failed that will allow clients to display custom error messages depending on the part intent. The processing and transfer-over-the-wire of this exception is to be implemented in coming changesets.