Misc. tweaks to vector slicing implementation

* Minor style/format changes

* Fix a signed/unsigned comparison compiler warning

* Use a non-fatal error for non-integral slice indices so we can
  report any further scripting errors instead of stopping the parse
  right there

src/Val.cc

@@ -3417,6 +3417,7 @@ bool VectorVal::Insert(unsigned int index, Val* element)
 		}
 
 	vector<Val*>::iterator it;
+
 	if ( index < val.vector_val->size() )
 		it = std::next(val.vector_val->begin(), index);
 	else