Started adding Restricted constraints stuff.
Added constraint methods for equivalence to TripleEqualsConstraints and its subtypes.
Moved default equality implicit back to Equality companion object. added a default implicit
in the Equivalence companion object too therefore. Did this to get the newly created generic TolerantEquivalence.tolerantEquivalence
to not be ambiguous with defaultEquality.
Get rid of some toVectors and other methods that don't exist in 2.9 for the 2.9 build.
Added RestrictedTripleEqualsSpec to 2.9 excludes for now.
Made the A <:< B forms of typeCheckedTripleEquals take an Equality[B] instead of an Equality[A] to
be consistent with typeRestrictedTripleEquals, and made A <:< B use an AToBeEqualityConstraint and
B <:< A use a BToAEqualityConstraint instead of BasicEqualityConstraints, for consistency with Equivalence ones.