Closes #140: More stable copy-to-repl interface, CL-free

* contrib/slime-repl.el (slime-repl): Return the REPL buffer switched to.
(slime-repl-copy-down-to-repl): New function.
(slime-inspector-copy-down-to-repl): Use `slime-repl-copy-down-to-repl'
(sldb-copy-down-to-repl): Use `slime-repl-copy-down-to-repl'

* contrib/swank-repl.lisp (*listener-saved-value*): New thread-global
variable.
(listener-save-value): Save values produced by slimefuns.
(listener-get-value): Get values saved by LISTENER-SAVE-VALUE.
(*last-repl-form*, *last-repl-values*, set-repl-variables): Deleted.
(repl-eval): Don't call SET-REPL-VARIABLES.