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.

mercurial/wireproto.py

@@ -585,7 +585,7 b' def _capabilities(repo, proto):'
             caps.append('stream')
         # otherwise, add 'streamreqs' detailing our local revlog format
         else:
-            caps.append('streamreqs=%s' % ','.join(requiredformats))
+            caps.append('streamreqs=%s' % ','.join(sorted(requiredformats)))
     if repo.ui.configbool('experimental', 'bundle2-advertise', True):
         capsblob = bundle2.encodecaps(bundle2.getrepocaps(repo))
         caps.append('bundle2=' + urllib.quote(capsblob))