Percent signs escaping in templatetags

Closes python-babel#43

In Django >= 1.9, `%` signs are escaped to `%%` during extraction
then replaced by `%` during the rendering. [1]

The extraction now behaves in the same way.

[1] django/django@b750889

django_babel/extract.py

@@ -112,10 +112,11 @@ def extract_django(fileobj, keywords, comment_tags, options):
                 else:
                     singular.append('%%(%s)s' % t.contents)
             elif t.token_type == TOKEN_TEXT:
+                contents = t.contents.replace('%', '%%')
                 if inplural:
-                    plural.append(t.contents)
+                    plural.append(contents)
                 else:
-                    singular.append(t.contents)
+                    singular.append(contents)
         else:
             if t.token_type == TOKEN_BLOCK:
                 imatch = inline_re.match(t.contents)
@@ -124,6 +125,7 @@ def extract_django(fileobj, keywords, comment_tags, options):
                 if imatch:
                     g = imatch.group(1)
                     g = strip_quotes(g)
+                    g = g.replace('%', '%%')
                     message_context = imatch.group(3)
                     if message_context:
                         # strip quotes

tests/test_extract.py

@@ -218,3 +218,13 @@ def test_blocktrans_with_whitespace_trimmed(self):
         buf = BytesIO(test_tmpl)
         messages = list(extract_django(buf, default_keys, [], {}))
         self.assertEqual([(4, None, u'foo bar', [])], messages)
+
+    def test_extract_trans_percents(self):
+        buf = BytesIO(b'{% trans "100% Bunny" %}')
+        messages = list(extract_django(buf, default_keys, [], {}))
+        self.assertEqual([(1, None, u'100%% Bunny', [])], messages)
+
+    def test_extract_blocktrans_percents(self):
+        buf = BytesIO(b'{% blocktrans %}100% Bunny{% endblocktrans %}')
+        messages = list(extract_django(buf, default_keys, [], {}))
+        self.assertEqual([(1, None, u'100%% Bunny', [])], messages)