Missing emacs-builds directory on a clean clone

Hi,

In this change the emacs-builds directory is created before performing the bzr checkout.

From the commit: "Without the directory the bzr build will tee to a non existing directory, subsequently the build will not happen."

I looked for a good place to put the statement, as it is in the build-emacs function, however I failed to find one so I added it the the bzr checkout script.

Hope this helps,

Arjen