wireproto: unescape argument names in batch command (BC)

Clients escape both argument names and values when using the
batch command. Yet the server was only unescaping argument values.

Fortunately we don't have any argument names that need escaped. But
that isn't an excuse to lack symmetry in the code.

Since the server wasn't properly unescaping argument names, this
means we can never introduce an argument to a batchable command that
needs escaped because an old server wouldn't properly decode its name.
So we've introduced an assertion to detect the accidental introduction
of this in the future. Of course, we could introduce a server
capability that says the server knows how to decode argument names and
allow special argument names to go through. But until there is a need
for it (which I doubt there will be), we shouldn't bother with adding
an unused capability.

mercurial/wireproto.py

@@ -191,6 +191,11 b' def encodebatchcmds(req):'
     """Return a ``cmds`` argument value for the ``batch`` command."""
     cmds = []
     for op, argsdict in req:
+        # Old servers didn't properly unescape argument names. So prevent
+        # the sending of argument names that may not be decoded properly by
+        # servers.
+        assert all(escapearg(k) == k for k in argsdict)
+
         args = ','.join('%s=%s' % (escapearg(k), escapearg(v))
                         for k, v in argsdict.iteritems())
         cmds.append('%s %s' % (op, args))
@@ -620,7 +625,7 b' def batch(repo, proto, cmds, others):'
         for a in args.split(','):
             if a:
                 n, v = a.split('=')
-                vals[n] = unescapearg(v)
+                vals[unescapearg(n)] = unescapearg(v)
         func, spec = commands[op]
         if spec:
             keys = spec.split()