when pushing a new branch over smart protocol, the source branch format get used even if the smart server's version of bazaar does not support it

[Benoit Pierre]

After registering a branch I tried to push my local version. The launchpad branch was created with the same format as the local branch: 1.9. The push completed without any error, but since the bzr version currently used by launchpad does not support this format, the result is an unusable branch.

The push should have failed with an error telling me that "format 1.9 is currently not supported", or completed with a warning telling me that the default (supported) format was used for the new branch.

Steps to reproduce:
- register a new hosted branch
- create a local branch with format 1.9
- push it to launchpad

=> push is successful, but the branch is unusable