Invalidate member caches in different periods
Invalidate member caches in different periods

A membercache is not valid in a period different from the one it was
created in. Reason: The denotations stored in the cache might have
different infos in different periods.

Also: add maybeOwner convenience method for printing, which handles
NoDenotation/NoSymbol gracefully.

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