Make .deb packages versioned

By adding a version number to debian package, it is possible
to easily rebuild packages of the same binary version;
e.g. HHVM 3.3.0 could be built as 3.3.0-1 and, if needed
(like because of bumped dependencies, also as 3.3.0-2 and so on.

Possible solution for #73 ([@ptarjan's comment](https://github.com/hhvm/packaging/issues/73#issuecomment-56874296)). Not tested, you may need to adjust the process a bit.