Mention value types in eqv documentation
Mention value types in eqv documentation

Add an example where eqv on Set objects is (counter-intuitively) false:
putting two objects which are equivalent each into a Set does not make
the Set objects equivalent. The explanation refers to documentation of
value types.

perl6/doc,perl6/doc,perl6/doc,MasterDuke17/doc,perl6/doc,tbrowder/doc,MasterDuke17/doc,MasterDuke17/doc,MasterDuke17/doc,tbrowder/doc,tbrowder/doc,perl6/doc,tbrowder/doc