500 when trying to import data from github

Hey people,

I noticed some lack of URL validation on the import script at: https://bitbucket.org/repo/import

If I set the URL to for example https://github.com/ikanobori/deposit it will throw a 500 error when I submit the form.

A helpful error message or the URL you actually want (the one pointing to the git repo itself) would be nice (or deduce it from the input github URL).