[gambit-list] Untested patch: Debugger command to reprint error

Since (IMO) the debugger should be able to describe everything it knows about, I wrote a new command (for version 4.2.2) to reprint the last error. Unfortunately I have no idea if I implemented it right. A patch is attached.

The test case foo bar ,d ,r implies that there's only one error shared by all REPL levels (which makes the levels less useful than they might be).

Typing the "foo bar" on the same line also shows how prompts and output can be mixed. The Emacs interface doesn't recognize the 1> prompt before the second error message, so it only highlights the first error even though the interpreter has forgotten the first error.

Thanks for any comments.

-- Derek