[svn r316] Fixed array slice assignments like: int[] arr = ...; arr[] = 42;

There was problems with most non basic types...
Added an option to premake so we can do: premake --target gnu --no-boehm
to disable the Boehm GC.

gen/classes.cpp

@@ -251,6 +251,7 @@ void DtoResolveClass(ClassDeclaration* cd)
     #else
         iri->vtblTy = isaStruct(itc->ir.vtblType->get());
     #endif
+        assert(iri->vtblTy);
 
         // set index
         iri->index = interIdx++;