Catch breaks.

As a result, C-c escapes to a no-module REPL rather than exiting.

Also:

- Since `read-eval-print-loop` already catches all non-break exceptions,
  wrapping it in `with-handlers` for `exn:fail?` is pointless; remove.

- Move some code out to new helper functions, `maybe-load-language-info`
  and `check-top-interaction`.