(scheme-trace-command, scheme-untrace-command)

(scheme-trace-command, scheme-untrace-command)
(scheme-macro-expand-command): New user options.
(scheme-trace-procedure, scheme-expand-current-form): New commands.
(scheme-form-at-point, scheme-start-file): New functions.
(run-scheme): Call `scheme-start-file' to get start file, and pass it to
`make-comint'.
(switch-to-scheme, scheme-proc): Call `scheme-interactively-start-process'
if no Scheme buffer/process is available.
(scheme-get-process): New function extracted from `scheme-proc'.
(scheme-interactively-start-process): New function.