bundle: avoid crash when no good changegroup version found When using treemanifests, only changegroup3 bundles can be created. However, there is currently no way of requesting a changegroup3 bundle, so we run into an assertion in changegroup.getbundler() when trying to get a changroup2 bundler. Let's avoid the traceback and print a short error message instead.

exchange: make _pushb2ctx() look more like _getbundlechangegrouppart() The functions already have a lot in common, but were structured a little differently.

exchange: get rid of "getcgkwargs" variable This also makes the "version" argument explicit (never relies on getlocalchangegroupraw()'s default), which I think is a good thing.

bundle: move writebundle() from changegroup.py to bundle2.py (API) writebundle() writes a bundle2 bundle or a plain changegroup1. Imagine away the "2" in "bundle2.py" for a moment and this change should makes sense. The bundle wraps the changegroup, so it makes sense that it knows about it. Another sign that this is correct is that the delayed import of bundle2 in changegroup goes away. I'll leave it for another time to remove the "2" in "bundle2.py" (alternatively, extract a new bundle.py from it).