bundle2: use a sorted dict for holding parameters

An upcoming change that introduces a 2nd part parameter to a part
reveals that `hg debugbundle` isn't deterministic because parameters
are stored on n plain, unsorted dict.

While we could change that command to sort before output, I think
the more important underlying issue is that bundle2 reading is taking
an ordered data structure and converting it to an unordered one.
Plugging in util.sortdict() fixes that problem while preserving API
compatibility.

This patch also appears to shine light on the fact that we don't
have tests verifying parts with multiple parameters roundtrip
correctly. That would be a good thing to test (and fuzz)... someday.

mercurial/bundle2.py

@@ -690,7 +690,7 b' class unbundle20(unpackermixin):'
 
     def _processallparams(self, paramsblock):
         """"""
-        params = {}
+        params = util.sortdict()
         for p in paramsblock.split(' '):
             p = p.split('=', 1)
             p = [urlreq.unquote(i) for i in p]
@@ -1115,8 +1115,8 b' class unbundlepart(unpackermixin):'
         self.mandatoryparams = tuple(mandatoryparams)
         self.advisoryparams  = tuple(advisoryparams)
         # user friendly UI
-        self.params = dict(self.mandatoryparams)
-        self.params.update(dict(self.advisoryparams))
+        self.params = util.sortdict(self.mandatoryparams)
+        self.params.update(self.advisoryparams)
         self.mandatorykeys = frozenset(p[0] for p in mandatoryparams)
 
     def _payloadchunks(self, chunknum=0):