bundle2: rename UnknownPartError to BundleValueError We are going to raise exceptions for a wider range of cases: unsupported mandatory stream and part parameters. We rename the exception with a wider name.

context: explicitly return a tuple In the refactoring of removing localrepo.status, 2edb8648c500, we accidentally changed the return type from a tuple to a list. Philosophically, this is incorrect so we explicitly return a tuple again.

wireproto: expose the list of getbundle arguments to extensions For now, getbundle accepts a fixed number of arguments: ``heads``, ``common`` and ``bundlecaps``. We make this list exposed at the module level to let extensions add content there. This is important for extensions that wish to use bundle2 for other contents than changegroup.

run-tests: write .err files earlier Earlier refactoring of run-tests.py accidentally broke --interactive and external diff generation by not having .err files written before they are consulted. This patch fixes that.

run-tests: exit with non-0 exit code when tests fail or warn As part of the run-tests.py refactor, run-tests.py accidentally started exiting with 0 for most test runs. This patch restores the expected behavior.

bundle2: expose mandatory params in a mandatorykeys attribute We expose all keys that MUST be processed in ``part.mandatorykeys``. This makes it much easier to access the information. Enforcement of the mandatory parameters is coming in later changesets.

bundle2: use the new ``part.params`` dictionary We use the new ``part.params`` dictionary to access the value of parameters instead of creating one from the part's attributes.