Fix for #371
Fix for #371

This causes backend to fail with ambiguous reference when loading
member "equals" of object "BoxesRuntime".

The reference is indeed ambiguous. BoxesRunTime has a two paremeter
equals method and, with the fix, inherits the one-parameter method from
Object. The backend needs to disambiguate, e.g. by demanding the `decl`
equals in BoxesRunTime instead of the member.

yusuke2255/dotty,auvik/dotty,folone/dotty,vsalvis/dotty,reactormonk/dotty,lampepfl/dotty,svalaskevicius/dotty,som-snytt/dotty,angi2/dotty,sjrd/dotty,sjrd/dotty,sjrd/dotty,lampepfl/dotty,som-snytt/dotty,svalaskevicius/dotty,som-snytt/dotty,angi2/dotty,spetz911/dotty,folone/dotty,lampepfl/dotty,densh/dotty,dotty-staging/dotty,lampepfl/dotty,spetz911/dotty,densh/dotty,vsalvis/dotty,sjrd/dotty,dotty-staging/dotty,VladimirNik/dotty,sjrd/dotty,auvik/dotty,som-snytt/dotty,dotty-staging/dotty,VladimirNik/dotty,reactormonk/dotty,lampepfl/dotty,yusuke2255/dotty,dotty-staging/dotty,dotty-staging/dotty,som-snytt/dotty