hgweb: generate archive links in order

It would be nice for archive links to always be in a certain commonly used
order, such as 'zip', 'bz', 'gzip2'. Repo index page (hgwebdir_mod) already
shows archive links in this order, let's do the same in hgweb_mod.

Sadly, archivespecs is a regular unordered dict, and collections.OrderedDict is
new in 2.7. But requestcontext.archives is a tuple of archive types, so it can
be used as an index to archivespecs.

mercurial/hgweb/hgweb_mod.py

@@ -134,7 +134,8 b' class requestcontext(object):'
 
     def archivelist(self, nodeid):
         allowed = self.configlist('web', 'allow_archive')
-        for typ, spec in self.archivespecs.iteritems():
+        for typ in self.archives:
+            spec = self.archivespecs[typ]
             if typ in allowed or self.configbool('web', 'allow%s' % typ):
                 yield {'type': typ, 'extension': spec[2], 'node': nodeid}