core,install: allow one more case of "instance propagation"

core,install: allow one more case of "instance propagation"

If we have a template unit template@.service, it should be allowed to specify a
dependency on a unit without an instance, bar@.service. When the unit is created,
the instance will be propagated into the target, so template@inst.service will
depend on bar@inst.service.

This commit changes unit_dependency_name_compatible(), which makes the manager
accept links like that, and unit_file_verify_alias(), so that the installation
function will agree to create a symlink like that, and finally the tests are
adjusted to pass.