Better C++ recognition

* ob-C.el: Added =C++= to =`org-babel-load-languages'=
automatically after loading =C=.
* org-src.el (org-src-lang-modes): Added association between
language =C++= and =`c++-mode'=.

=C++= is added to org-babel-load-languages to make
`org-babel-demarcate-block' recognize =C++= as a proper language.

lisp/ob-C.el

@@ -39,6 +39,8 @@
 
 (defvar org-babel-tangle-lang-exts)
 (add-to-list 'org-babel-tangle-lang-exts '("C++" . "cpp"))
+(let ((x (member '(C . t) org-babel-load-languages)))
+  (setcdr x  (cons '(C++ . t) (subseq x 1))))
 
 (defvar org-babel-default-header-args:C '())
 

lisp/org-src.el

@@ -179,7 +179,7 @@ but which mess up the display of a snippet in Org exported files.")
 (defcustom org-src-lang-modes
   '(("ocaml" . tuareg) ("elisp" . emacs-lisp) ("ditaa" . artist)
     ("asymptote" . asy) ("dot" . fundamental) ("sqlite" . sql)
-    ("calc" . fundamental) ("C" . c) ("cpp" . c++)
+    ("calc" . fundamental) ("C" . c) ("cpp" . c++) ("C++" . c++)
     ("screen" . shell-script))
   "Alist mapping languages to their major mode.
 The key is the language name, the value is the string that should