EquivalentValue: Remove getDeepestValue().

Add check at constructor so that we never get EquivalentValue inside.
This renders (original buggy) getDeepestValue() obsolete.
Equivalent.Equivalent(): Use if instead of while since we never get nested EquivalentValues.
EquivalentValue: add back getDeepestValue(), add deprecated tag.
Merge pull request #158 from wishstudio/develop

EquivalentValue: Remove getDeepestValue().