Fix up password reset template to use modern CSRF protection.

Once upon a time, we rolled our own CSRF protection. This file was somehow
never updated for it, and still had a comment about what we should do when
moving to Django 1.2(!).

Testing done:
Went through complete password reset flow.

Reviewed at https://reviews.reviewboard.org/r/6405/
Merge branch 'release-2.0.x'