D17 was reverted because it broke creating bundle for non-general delta repos.
The reason is the following: D17 made infinitepush extension override
changegroup.supportedoutgoingversion() function and discard '01' version.
For non-general delta repositories it resulted in broken hg bundle ...
command.
abort: repository does not support bundle version 01
This diff fixes it by not overriding supportedoutgoingversion(). Instead
getscratchbranchpart() has its own logic of selecting changegroup version.
Does this mean the tests are testing the case where changegroup3 is disabled? Seems like we want that coverage since our normal devserver/hg server communication doesn't use changegroup3 right?