Single stepping through code from Emacs

Single stepping through code from Emacs

When you use GDS to evaluate Scheme code from Emacs, you can now use
`C-u' to indicate that you want to single step through that code. See
`Evaluating Scheme Code' in the manual for more details.

	* scheme-using.texi (Evaluating Scheme Code): Document use of
        `C-u' prefix with evaluation commands.

        * gds-scheme.el (gds-eval-region, gds-eval-expression)
        (gds-eval-defun, gds-eval-last-sexp): Support `C-u' prefix,
        meaning that user wants to single step through the code.

        * gds-client.scm (handle-nondebug-protocol): Add support for
        setting a trap on code that is about to be evaluated.