debugbundle: display the content of obsmarkers parts We parse and display the markers in the part when possible.

bundle: add an experimental knob to include obsmarkers in bundle The "hg bundle" command is a good place to test if the inclusion of obsmarkers within a bundle is working well (part exists, content is correct etc). So we add a way to have them included. Ideally, this would be controlled by a change around bundlespec (bundlespec "v3" + arguments). However, my main goal is to have obsmarkers included in bundle created by the 'hg strip' command, not the 'hg bundle' so for now I'm avoiding the detour through bundlespec rework territory. Better debug output for obsmarkers in 'debugbundle' will be added in later changesets. The 'test-obsolete-bundle-strip.t' test will also get updated in a later changeset to keep the current changeset smaller.

bundle2: move function building obsmarker-part in the bundle2 module We move it next to similar part building functions. We will need it for the "writenewbundle" logic. This will allow us to easily include obsmarkers in on-disk bundle, a necessary step before having `hg strip` also operate on markers. (Yes, the bundle2 module was already too large, but there any many interdependencies between its components so it is non-trivial to split, this is a quest for another adventure.)

policy: remove unused policynoc and policynocffi constants