* lisp/erc/erc-ring.el: (erc-add-to-input-ring)
(erc-previous-command): Use existing API to grab input.
* test/lisp/erc/erc-tests.el: (erc-ring-previous-command)
See (bug#46339).
* lisp/erc/erc.el (erc--unignore-user): Separate into own function
(bug#40137).
(erc-cmd-IGNORE): Ask if the user wants a timeout.
(erc--read-time-period): New function.