Switch further simple types (sets, enums, class references, pointers) to indirect type information (again without breaking backwards compatibility).

compiler/ncgrtti.pas, TRTTIWriter.write_rtti_data:
  * enumdef_rtti, setdef_rtti, classrefdef_rtti & pointerdef_rtti: write an indirect RTTI reference

rtl/objpas/typinfo.pp, TTypeData:
  * rename BaseType to BaseTypeRef, CompType to CompTypeRef, InstanceType to InstanceTypeRef and RefType to RefTypeRef and change their type to TypeInfoPtr
  + add properties BaseType, CompType, InstanceType & RefType which return a PTypeInfo out of the corresponding *Ref field depending on the compiler version

git-svn-id: http://svn.freepascal.org/svn/fpc/branches/svenbarth@28265 3ad0048d-3df7-0310-abae-a5850022a9f2