Marked bytestrings with b prefix. Refs #18269

This is a preparation for unicode literals general usage in
Django (Python 3 compatibility).

tests/regressiontests/templates/unicode.py

@@ -10,16 +10,16 @@ class UnicodeTests(TestCase):
         t1 = Template(u'ŠĐĆŽćžšđ {{ var }}')
         # Templates can also be created from bytestrings. These are assumed to
         # be encoded using UTF-8.
-        s = '\xc5\xa0\xc4\x90\xc4\x86\xc5\xbd\xc4\x87\xc5\xbe\xc5\xa1\xc4\x91 {{ var }}'
+        s = b'\xc5\xa0\xc4\x90\xc4\x86\xc5\xbd\xc4\x87\xc5\xbe\xc5\xa1\xc4\x91 {{ var }}'
         t2 = Template(s)
-        s = '\x80\xc5\xc0'
+        s = b'\x80\xc5\xc0'
         self.assertRaises(TemplateEncodingError, Template, s)
 
         # Contexts can be constructed from unicode or UTF-8 bytestrings.
-        c1 = Context({"var": "foo"})
-        c2 = Context({u"var": "foo"})
-        c3 = Context({"var": u"Đđ"})
-        c4 = Context({u"var": "\xc4\x90\xc4\x91"})
+        c1 = Context({b"var": b"foo"})
+        c2 = Context({u"var": b"foo"})
+        c3 = Context({b"var": u"Đđ"})
+        c4 = Context({u"var": b"\xc4\x90\xc4\x91"})
 
         # Since both templates and all four contexts represent the same thing,
         # they all render the same (and are returned as unicode objects and