view mercurial/__init__.py @ 26395:4e7b0bf9f0b1

unbundle20: allow registering handlers for stream level parameters

As a comment in the code have been asking for, it is now possible to register
piece of code that handle parameters for the stream. I've been wondering is such
function should be class methods or not. I eventually went for externally
decorated methods to stick with the culture of extensibility from an extensions
that apply to bundle2.