* module/system/repl/repl.scm (default-pre-unwind-handler)
(default-catch-handler): New procedures, to do some error handling in
the repl.
(start-repl): Catch errors in the repl loop.
* module/system/base/compile.scm (<cenv>): No more cenv, it was a useless
data structure.
* module/system/repl/command.scm (*command-table*): Remove `use', it's
the same as `import'. Otherwise in this file, adapt to the repl having
direct pointers to the vm and the language, and to the module being in
the current-module fluid.
* module/system/repl/repl.scm (prompting-meta-read):
* module/system/repl/common.scm (<repl>): The repl now has a direct
pointer to the vm and language. Adapt accordingly.
* module/system/repl/common.scm (repl-prompt): Return a string instead of
outputting to the port, for better readline integration.
* module/system/repl/repl.scm (meta-reader, prompting-meta-read)
(start-repl): Integrate with (ice-9 readline) via the current-reader
fluid and the repl-reader function, both from boot-9.scm.
* module/system/repl/command.scm (system): Declare exports in the module
declaration.
* module/system/repl/repl.scm (start-repl): If the evaluation returns
multiple values, print them separately.
