Previously:

 - "build-depends" entries on internal libraries with an explicit version
   range are an error.

Now for all three of "build-tools", "tool-depends", and "build-depends":

 - Explicit versions ranges on internal components that are satisfied by
   the current package cause a warning.

 - Explicit version ranges on internal components are are not satisfied by
   the current package are an error.

And additionally for "tool-depends":

 - dependencies on a non-existent executable in the current package are an
   error.