fix bug #23113 unit-specific anims missing (tutorial delfador)

There were two bugs here:
In 6603de667b464d6f6bea04fa07dd25ac8493bc39, in unit::advance_to,
the code fragment that resets the animation set based on the new
unit type was made to run after modifications had been processed.
Since modifications may introduce new animations, this caused these
to be discarded.

In d7bf5be356d71ada4f8b657671258160095d5fe3, [animate_unit] was
broken by accidentally not including it in the lua kernel
initialization routine.
Merge branch 'master' of https://github.com/wesnoth/wesnoth