Introduce invariant that _invalid_pofile() takes unicode line.

This makes debugging and reasoning about the code easier;
otherwise it is surprising that sometimes `line` is a unicode
and sometimes not.

So far, when it was not, it could either be only `""` or
`'Algo esta mal'`; thus this commit makes those two u"" strings.
In all other cases, it was guaranteed that it's unicode,
because all code paths leading to `_invalid_pofile()` went through

    if not isinstance(line, text_type):
        line = line.decode(self.catalog.charset)

before.

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/messages/test_pofile.py b/tests/messages/test_pofile.py
index e77fa6e..214ddf5 100644
--- a/tests/messages/test_pofile.py
+++ b/tests/messages/test_pofile.py
@@ -480,7 +480,7 @@ msgstr[2] "Vohs [text]"
     def test_invalid_pofile_with_abort_flag(self):
         parser = pofile.PoFileParser(None, abort_invalid=True)
         lineno = 10
-        line = 'Algo esta mal'
+        line = u'Algo esta mal'
         msg = 'invalid file'
         with self.assertRaises(pofile.PoFileError) as e:
             parser._invalid_pofile(line, lineno, msg)