encoding: use range() instead of xrange()

Python 3 doesn't have xrange(). Instead, range() on Python 3
is a generator, like xrange() is on Python 2.

The benefits of xrange() over range() are when there are very
large ranges that are too expensive to pre-allocate. The code
here is only creating <128 values, so the benefits of xrange()
should be negligible.

With this patch, encoding.py imports safely on Python 3.

mercurial/encoding.py

@@ -387,8 +387,8 b' class normcasespecs(object):'
     other = 0
 
 _jsonmap = []
-_jsonmap.extend("\\u%04x" % x for x in xrange(32))
-_jsonmap.extend(chr(x) for x in xrange(32, 127))
+_jsonmap.extend("\\u%04x" % x for x in range(32))
+_jsonmap.extend(chr(x) for x in range(32, 127))
 _jsonmap.append('\\u007f')
 _jsonmap[0x09] = '\\t'
 _jsonmap[0x0a] = '\\n'
@@ -400,7 +400,7 b' class normcasespecs(object):'
 _paranoidjsonmap = _jsonmap[:]
 _paranoidjsonmap[0x3c] = '\\u003c'  # '<' (e.g. escape "</script>")
 _paranoidjsonmap[0x3e] = '\\u003e'  # '>'
-_jsonmap.extend(chr(x) for x in xrange(128, 256))
+_jsonmap.extend(chr(x) for x in range(128, 256))
 
 def jsonescape(s, paranoid=False):
     '''returns a string suitable for JSON