Added pending deprecation to prefix for solid_i18n_patterns.

[julianwachholz]

Fixes #8

I removed the now unsupported Django version 1.5 as well as Python version 3.2 from the tox.ini. I didn't modify travis.yml however.

[coveralls]

Coverage increased (+0.22%) when pulling 98b8d75 on julianwachholz:issue8 into dcdaa6d on st4lk:master.

[st4lk]

Julian, thanks for this pull request!
It surely useful and make this package to be up to date.
But i'll need some more time to investigate the code of this request and of django v1.8 (that is currently not released).
Maybe it is better to wait for official django v1.8 release before implementing such functionality.
Currently official django version is 1.7.x, and in corresponding branch there is no warning about prefix:
https://github.com/django/django/blob/stable/1.7.x/django/conf/urls/__init__.py#L44

I suppose, such warning will be shown only in django v1.8+ versions:
https://github.com/django/django/blob/master/django/conf/urls/__init__.py#L46

As is said before, i think it is better to wait for official v1.8 release. And also i think we must implement this optional prefix functionality only if django version is greater or equal to v1.8, and not in earlier versions. So we'll need some if conditions to check currently installed django version.

[julianwachholz]

I don't think it's required to implement a version switch of this feature alone, only the warning should be raised in 1.8+ only.

I'm okay with postponing this until a 1.8 release, as that will also be a LTS version.