formatter: support json formatting of long type

By luck, we appear to not pass any long instances into
the JSON formatter. I suspect this will change with all the
Python 3 porting work. Plus I have another series that will
convert some ints to longs that triggers this.

mercurial/formatter.py

@@ -295,7 +295,7 b' def _jsonifyobj(v):'
         return 'true'
     elif v is False:
         return 'false'
-    elif isinstance(v, (int, float)):
+    elif isinstance(v, (int, long, float)):
         return str(v)
     else:
         return '"%s"' % encoding.jsonescape(v)