use default repository when no url specified

When using the deploy goal there is no need to specify the url of the repository.

When using deploy-file you DO need to specify the url. This is a problem, because during development I like to deploy to snapshot repository and when releasing i deploy to release repository and I can't add this logic to the pom.

Thas is why I like the url paramter to become optional (backwards compatible) and add default behaviour when it is null. It should just like the deploy plugin use the default repository. Snapshot for snapshots and release for none snapshot versions.

I added a patch file fixing this.
I also added complete source of patched Mojo