code: private boolean weHaveVar( String name )
      {
          // super.variables.containsKey( name ) not any faster, I checked
          try {
              return super.getVariableImpl( name, false ) != null;
          } catch ( UtilEvalError e ) { return false; }
      }
docs: We have the variable: either it was declared here with a type, giving
  it block local scope or an untyped var was explicitly set here via
  setBlockVariable().