Also removed RefExpr::Eval(Val*) method since it was never called
(Clang emitted warning about this hiding overloaded virtual function
UnaryExpr::Eval(Frame*)) and doesn't appear to be necessary even if it
was called to avoid the default vector handling of UnaryExpr::Eval
(as the comment suggests as the intention).
The communication subsystem is now disabled until a new BiF,
enable_communication(), is called. The base scripts do this
automatically when either a Communication::Node is defined, or Bro is
asked to listen for incoming connections.
"delete x$y" now resets record field "x" back to its original state if
it is either &optional or has a &default. "delete" may not be used
with non-optional/default fields.