Fix (or document) lower-casing behavior of title filter

[Tim Graham]

The following seems unexpected to me, although there may be use cases where it's expected behavior (e.g. if you have all capitalized text and want it titled). See also #21299.

>>> from django.template.defaultfilters import title
>>> title("ABC News")
u'Abc News'

[Baptiste Mispelon]

That behavior is consistent with python's str.title method [1].

Django's title function has two features on top of str.title:

• title("isn't it") == "Isn't It" (whereas "isn't it".title() == "Isn'T It)
• title("8foo") == "8foo" (whereas "8foo".title() == "8Foo")

I don't think we can fix this particular issue without breaking backwards-compatibility so I think documenting it is the best course of action.

[1] ​http://docs.python.org/2/library/stdtypes.html?highlight=str.title#str.title

[Tim Graham <timograham@…>]

In eafe279120e7e6ebe7b6d42443366088ba1a50c8:

Fixed #21306 -- Documented lower-casing behavior of title filter.

[Tim Graham <timograham@…>]

In d774cb219c4581461bd2310450605916dd7c13e6:

[1.6.x] Fixed #21306 -- Documented lower-casing behavior of title filter.

Backport of eafe279120 from master