Pass 'current_app' when rendering view names

When using namespaced URLs, passing `current_app` lets `reverse` know
which app instance to use.

If `current_app` isn't passed -- and the view name doesn't use the
namespace directly -- the URL is reversed to the last registered
instance.

With this commit, the request's current namespace is passed to
`reverse`.
Merge pull request #8 from edavis/master

Pass 'current_app' when rendering view names