json: avoid extra string manipulation of dict keys

A key must be string per JSON spec, and that's also true for template dicts.

mercurial/templatefilters.py

@@ -234,7 +234,7 b' def json(obj, paranoid=True):'
     elif isinstance(obj, bytes):
         return '"%s"' % encoding.jsonescape(obj, paranoid=paranoid)
     elif util.safehasattr(obj, 'keys'):
-        out = ['%s: %s' % (json(k), json(v))
+        out = ['"%s": %s' % (encoding.jsonescape(k, paranoid=paranoid), json(v))
                for k, v in sorted(obj.iteritems())]
         return '{' + ', '.join(out) + '}'
     elif util.safehasattr(obj, '__iter__'):