Add comment to explain IsNonAtomicComponentObjectRep etc.

... they are used by HPC-GAP, and in GAP do nothing different than their
counterparts, namely:
  IsNonAtomicComponentObjectRep <-> IsComponentObjectRep
  IsReadOnlyPositionalObjectRep <-> IsPositionalObjectRep
  IsAtomicPositionalObjectRep   <-> IsPositionalObjectRep

We mainly provide them in plain GAP to make it easier to write code
that works well in both GAP and HPC-GAP.

lib/type.g

@@ -309,6 +309,8 @@ DeclareRepresentation( "IsPositionalObjectRep", IS_OBJECT, [], IS_OBJECT );
 DeclareRepresentation( "IsComponentObjectRep", IS_OBJECT, [], IS_OBJECT );
 DeclareRepresentation( "IsDataObjectRep", IS_OBJECT, [], IS_OBJECT );
 
+# the following are for HPC-GAP, but we also provide them in plain GAP, to
+# make it easier to write code which works in both.
 DeclareRepresentation( "IsNonAtomicComponentObjectRep",
         IsComponentObjectRep, [], IS_OBJECT); 
 DeclareRepresentation( "IsReadOnlyPositionalObjectRep",