filepath_to_uri raises UnicodeDecodeError on utf8 input

[Ivan Virabyan]

The docs say "The path is assumed to be either UTF-8 or unicode." in ​https://docs.djangoproject.com/en/1.5/ref/utils/#django.utils.encoding.filepath_to_uri:

>>> filepath_to_uri('тест')
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/kanobu/env/lib/python2.7/site-packages/django/utils/encoding.py", line 235, in filepath_to_uri
    return quote(force_bytes(path.replace("\\", "/")), safe=b"/~!*()'")
UnicodeDecodeError: 'ascii' codec can't decode byte 0xd0 in position 0: ordinal not in range(128)

Since the module django.utils.encoding uses unicode literals, code path.replace("\", "/") fails, because it tries to decode path

[Ivan Virabyan]

fix with tests

[Claude Paroz]

A variant patch (python 3 compatible)

[Claude Paroz <claude@…>]

In 164528acc8752f33a3af4c1255b24702a4c81240:

Fixed #20108 -- Fixed filepath_to_uri decoding error

This was a regression due to unicode_literals usage. Thanks Ivan
Virabyan for the report and the initial patch.

[Claude Paroz <claude@…>]

In deec020bf5927abbdd667912f80794c32c03e609:

[1.5.x] Fixed #20108 -- Fixed filepath_to_uri decoding error

This was a regression due to unicode_literals usage. Thanks Ivan
Virabyan for the report and the initial patch.
Backport of 164528acc8 from master.