debugger: fix environment bug and remove confirmation at quit

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14379 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
test/tool-debugger: add simple test for the debugger

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14381 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02