Strip ubuntu and build version suffix when present

In Ubuntu, this package's version may contain the suffix ubuntuX or buildX, e.g. 3.10-2build4.

We patched the d/control file so that the VERSION variable strips those values whenever they are present. I would like to include this mechanism in the Debian package d/rules file as well, so that this package and the Ubuntu one are always in sync with new releases automatically.