I've replaced the versioned Replaces with an unversioned one as they aren't any packages with a higher version (as the package got renamed).
For libxen3-dev:
I guess the Replaces should be on libxen3.0-dev instead of libxen3.0 and I've added libxen3.1-dev and libxen3.2-dev to Conflicts (as it's described in the Debian policy manual for replacing whole packages).
I didn't add libxen3.1 to Conflicts for libxen3 as I'm not sure if it's correct.
I didn't subscribe u-m-s for sponsoring as I don't know if this bug is important enough to get an exception right now.
Here is a debdiff for it:
I've replaced the versioned Replaces with an unversioned one as they aren't any packages with a higher version (as the package got renamed).
For libxen3-dev:
I guess the Replaces should be on libxen3.0-dev instead of libxen3.0 and I've added libxen3.1-dev and libxen3.2-dev to Conflicts (as it's described in the Debian policy manual for replacing whole packages).
I didn't add libxen3.1 to Conflicts for libxen3 as I'm not sure if it's correct.
I didn't subscribe u-m-s for sponsoring as I don't know if this bug is important enough to get an exception right now.