bundlespec: handle the presence of obsmarker part This make `hg debugbundle --spec` more informative about extra part in the bundle.

bundlespec: fix the generation of bundlespec for `cg.version` If the value is non-default, we display it.

bundlespec: allow the bundle spec to control the bundle version This makes it possible to create bundle using changelog-v3. The `hg debugbundle --spec` output is borked, but this will be fixed in coming changesets.

bundlespec: do not check for `-` in the params portion of the bundlespec Otherwise bundle parameter with `-` in their names result in a crash.

bundlespec: add processing of some parameter value The boolean option needs to be turned into boolean.

bundlespec: extract the parseparams closure It has no value being a closure. We extract it before modifying it further.

bundlespec: test `no` value for the `obsolescence` parameter This is currently broken, but let us test for it first.

bundlespec: test that parameter overwrite the local config This is currently working, but havint it explicitly tested seems useful.

bundlespec: do not overwrite bundlespec value with the config one This is finally making the `obsolete` bundlespec paramater work.

bundlespec: add a `overwrite` parameter to set_param This will open the way for the configuration value to yield in front of the explicit bundle type.