ob-ruby: Fix ruby tests

* lisp/ob-ruby.el (org-babel-ruby-prompt):
(org-babel-ruby-define-prompt): New variables used to set appropriate
unique prompt and disable echo in session.
(org-babel-ruby-initiate-session): Setup prompt and echo during
session initialization.
(org-babel-ruby-evaluate): Rely on `org-babel-ruby-initiate-session'
to setup prompt and echo.  Re-setting the prompt back after every
evaluation can be tricky because of async nature of the prompt, so it
is now dropped.

lisp/ob-ruby.el

@@ -152,10 +152,16 @@ Emacs-lisp table, otherwise return the results as a string."
   (let ((res (org-babel-script-escape results)))
     (if (listp res)
         (mapcar (lambda (el) (if (not el)
-				 org-babel-ruby-nil-to el))
+			    org-babel-ruby-nil-to el))
                 res)
       res)))
 
+(defvar org-babel-ruby-prompt "_org_babel_ruby_prompt "
+  "String used for unique prompt.")
+
+(defvar org-babel-ruby-define-prompt
+  (format  "IRB.conf[:PROMPT][:CUSTOM] = { :PROMPT_I => \"%s\" }" org-babel-ruby-prompt))
+
 (defun org-babel-ruby-initiate-session (&optional session params)
   "Initiate a ruby session.
 If there is not a current inferior-process-buffer in SESSION
@@ -166,6 +172,7 @@ then create one.  Return the initialized session."
 			     (assoc inf-ruby-default-implementation
 				    inf-ruby-implementations))))
 	   (buffer (get-buffer (format "*%s*" session)))
+           (new-session? (not buffer))
 	   (session-buffer (or buffer (save-window-excursion
 					(run-ruby-or-pop-to-buffer
 					 (if (functionp command)
@@ -176,16 +183,30 @@ then create one.  Return the initialized session."
 					   (inf-ruby-buffer)))
 					(current-buffer)))))
       (if (org-babel-comint-buffer-livep session-buffer)
-	  (progn (sit-for .25) session-buffer)
+	  (progn
+            (sit-for .25)
+            ;; Setup machine-readable prompt: no echo, prompts matching
+            ;; uniquely by regexp.
+            (when new-session?
+              (with-current-buffer session-buffer
+                (setq-local comint-prompt-regexp (concat "^" org-babel-ruby-prompt))
+                (insert org-babel-ruby-define-prompt ";")
+                (insert "_org_prompt_mode=conf.prompt_mode;conf.prompt_mode=:CUSTOM;")
+                (insert "conf.echo=false")
+                (comint-send-input nil t)))
+            session-buffer)
 	(sit-for .5)
 	(org-babel-ruby-initiate-session session)))))
 
 (defvar org-babel-ruby-eoe-indicator ":org_babel_ruby_eoe"
   "String to indicate that evaluation has completed.")
+
 (defvar org-babel-ruby-f-write
   "File.open('%s','w'){|f| f.write((_.class == String) ? _ : _.inspect)}")
+
 (defvar org-babel-ruby-pp-f-write
   "File.open('%s','w'){|f| $stdout = f; pp(results); $stdout = orig_out}")
+
 (defvar org-babel-ruby-wrapper-method
   "
 def main()
@@ -194,6 +215,7 @@ end
 results = main()
 File.open('%s', 'w'){ |f| f.write((results.class == String) ? results : results.inspect) }
 ")
+
 (defvar org-babel-ruby-pp-wrapper-method
   "
 require 'pp'
@@ -237,7 +259,6 @@ return the value of the last statement in BODY, as elisp."
 	 (org-babel-comint-with-output
 	     (buffer org-babel-ruby-eoe-indicator t eoe-string)
 	   (insert eoe-string) (comint-send-input nil t))
-	 ;; Now we can start the evaluation.
 	 (mapconcat
 	  #'identity
 	  (butlast
@@ -246,14 +267,9 @@ return the value of the last statement in BODY, as elisp."
 	     #'org-trim
 	     (org-babel-comint-with-output
 		 (buffer org-babel-ruby-eoe-indicator t body)
-	       (mapc
-		(lambda (line)
-		  (insert (org-babel-chomp line)) (comint-send-input nil t))
-		(list "conf.echo=false;_org_prompt_mode=conf.prompt_mode;conf.prompt_mode=:NULL"
-		      body
-		      "conf.prompt_mode=_org_prompt_mode;conf.echo=true"
-		      eoe-string)))
-	     "\n") "[\r\n]") 4) "\n")))
+               (insert (org-babel-chomp body) "\n" eoe-string)
+               (comint-send-input nil t))
+	     "\n") "[\r\n]")) "\n")))
       (`value
        (let* ((tmp-file (org-babel-temp-file "ruby-"))
 	      (ppp (or (member "code" result-params)