[bug 821898] Master gitmo

This set of commits switches us to using git.mozilla.org.  The first commit looks really large, but it's just parsing and re-serializing the manifest using lxml (based on libxml2).  The resulting XML has been tested to work with repo by syncing down a whole tree.


There is another commit that switches us to using the git.mozilla.org remote and another which removes the redundant github.com/mozilla-b2g (but leaves github.com/mozilla).

One question I have is whether we should be adding the b2g/ and releases/ prefixes to the project's name attribute or the remote's fetch URL and having two git.mozilla.org remotes.  Which do you prefer?

This bug is blocking-basecamp+