[Java] Used LinkedHashSet to preserve insertion order in SemanticContext

[jcking]

Currently SemanticContext equality and hashing assume a well defined iteration order for HashSet. HashSet does not actually guarantee this, so we need to switch to LinkedHashSet which guarantees iteration order based insertion order.

[jcking]

@parrt

[parrt]

I think I'm going to need time to look at this in more detail after 4.10. should be okay but you never know...