util: fix sortdict.update() to call __setitem__() on PyPy (issue5639)

It appears that overriding __setitem__() doesn't work as documented on PyPy.
Let's patch it as before bd0fd3ff9916.

https://docs.python.org/2/library/collections.html#ordereddict-examples-and-recipes

The issue was ui.configitems() wasn't ordered correctly, so the pull command
was wrapped in different order.

mercurial/pycompat.py

@@ -16,6 +16,7 b' import shlex'
 import sys
 
 ispy3 = (sys.version_info[0] >= 3)
+ispypy = (r'__pypy__' in sys.builtin_module_names)
 
 if not ispy3:
     import cookielib

mercurial/util.py

@@ -584,6 +584,14 b' class sortdict(collections.OrderedDict):'
             del self[key]
         super(sortdict, self).__setitem__(key, value)
 
+    if pycompat.ispypy:
+        # __setitem__() isn't called as of PyPy 5.8.0
+        def update(self, src):
+            if isinstance(src, dict):
+                src = src.iteritems()
+            for k, v in src:
+                self[k] = v
+
 @contextlib.contextmanager
 def acceptintervention(tr=None):
     """A context manager that closes the transaction on InterventionRequired