#18 treat relations 'has' and 'is' specially

[Ronald Denaux]

Relationships 'is' and 'has' should be excluded from Rabbit. These are used in natural language in different cases which are difficult to disambiguate. In some of the example ontologies of Ordance Survery, the 'has' relation is used in the following way:

'No Backwater has a Current' should be translated as not (hasCurrent some Current). This current parser would require the user to define relationship 'has' which would be very generic. Rabbit could interpret pattern 'has' <object> as requiring a method 'has current'. The 'has' relation would still exist, but it would be part of the Rabbit language. 'has current' would be a subproperty of 'has', with 'Current' as its range.