Moving hg repo to git doesn't update Project.repo_type

[agjohnson]

If you had a project connected to an hg repo, and then you update the project's remote repo to a Git repository, the project gets stuck in a state where it can't build. Here's an example:

https://readthedocs.org/projects/yaml/builds/26717412/

The admin shows the right value, but this must just be the display of the field. The raw value doesn't match:

In [1]: project = Project.objects.get(slug='yaml')
Out[1]: <Project: yaml>

In [2]: proj.repo_type
Out[2]: 'hg'

I had manually:

project.repo_type = 'git'
project.save()