Made firearms list portable

"erc-firearms.el" is not "firearms.sexp", and can be `read' by any
lisp that implements the `vector' function.
Made firearms non-portable, but safer

The firearms file is now a file containing a single vector which can
be `read' in.  The portable format had to be `eval'd because different
lisps use different syntax for (self-evaluating) vectors, which is
less safe.