* lisp/ob-scheme.el (org-babel-scheme-execute-with-geiser): Return
"#<void>" or "#<unspecified>" when the REPL says so.
* testing/lisp/test-ob-scheme.el (test-ob-scheme/unspecified): New
test.
(test-ob-scheme/prologue): Fix tests.
Reported-by: Lawrence Bottorff <borgauf@gmail.com>
<http://lists.gnu.org/archive/html/emacs-orgmode/2017-09/msg00346.html>