Fixed assertion: nortcheck ---> no_rtcheck
- Modified internal representation of assertions (assertion_db/10), to have the
  properties in the body of a fake clause assertion_head/6, such that analyzers
  can report results about the assertions calling the properties.

- Renamed kbtext:nocheck to kbtext:nocheck_db, to avoid clashes with
  prosynprops:nocheck
Added nativeprops.pl, to override the one in SWI-Prolog
Minor bug fix: Module var was unbound
- Increased precision of location, by using $source_location and adding an extra
  argument to assertion_head/7 containing the subterm position of the assertion
  head