configitems: register the 'server.preferuncompressed' config

mercurial/configitems.py

@@ -131,6 +131,9 b" coreconfigitem('server', 'disablefullbun"
 coreconfigitem('server', 'maxhttpheaderlen',
     default=1024,
 )
+coreconfigitem('server', 'preferuncompressed',
+    default=False,
+)
 coreconfigitem('ui', 'clonebundleprefers',
     default=list,
 )

mercurial/wireproto.py

@@ -755,7 +755,7 b' def _capabilities(repo, proto):'
     # copy to prevent modification of the global list
     caps = list(wireprotocaps)
     if streamclone.allowservergeneration(repo):
-        if repo.ui.configbool('server', 'preferuncompressed', False):
+        if repo.ui.configbool('server', 'preferuncompressed'):
             caps.append('stream-preferred')
         requiredformats = repo.requirements & repo.supportedformats
         # if our local revlogs are just revlogv1, add 'stream' cap