redundant string comparators deleted
Implement Default prefix manager in prefix ontology format objects
cannot be overriden #9
removed unnecessary finals
Add @Nonnull and @Nonnegative annotations to OWLAPIPreconditions
Remove no argument constructor from OwlOntologyChangeRecord.

Java Serialization only requires a no-arg constructor on the first *non*-Serializable superclass of a serialized Object.
Since OwlOntologyChangeRecord is serializable, it does not need the no-arg constructor.
merge remove_noarg_constructor_from_change_record
Annotate  fields in OWLOntologyChangeRecord as Nonnull
Merge branch 'version4' into owlapi-api-nullity

Conflicts:
	api/src/main/java/org/semanticweb/owlapi/change/ConvertEquivalentClassesToSuperClasses.java
	api/src/main/java/org/semanticweb/owlapi/formats/PrefixOWLOntologyFormat.java
	api/src/main/java/org/semanticweb/owlapi/util/DefaultPrefixManager.java
	api/src/main/java/org/semanticweb/owlapi/util/OWLAPIPreconditions.java
	impl/src/main/java/uk/ac/manchester/cs/owl/owlapi/OWLImmutableOntologyImpl.java
	parsers/src/main/java/org/semanticweb/owlapi/krss2/renderer/KRSS2OWLObjectRenderer.java
	parsers/src/main/java/org/semanticweb/owlapi/krss2/renderer/KRSSObjectRenderer.java
Annotate more fields as nonnull
Annotate more fields as nonnull