stream: sort stream capability before serialisation We want that capability to be stable in our testing. This is currently not an issue because the set is size 1, but this will be once generaldelta related data gets in there.

test: spread capabilities replies in 'test-hgweb-commands' Any changes to the capabilities string was very hard to review. So we introduce two tests. A small one that validates the format and a second one to validate the content, where each capability is on its own line to make changes simpler to review.