[Orgmode] [babel] problems with org-babel-src-block-regexp

[Maurizio Vitale]

There're problems with org-babel-src-block-regexp when the src block
contains the block delimiters (for instance in strings or comments).

Granted, this is an uncommon occurrence (which I discovered by accident)
editing an org-file containing elisp code that needed to insert
#+begin_src...#+end_src pairs, but if it is not too difficult to fix it
would be nice to have a more useful behaviour.

This is my setting:
org-babel-src-block-regexp is a variable defined in `org-babel.el'.
Its value is 
"^[     ]*#\\+begin_src[        ]+\\(python\\|sh\\|emacs-lisp\\)[       
]*\\([^\":\n]*\"[^\"\n*]*\"[^\":\n]*\\|[^\":\n]*\\)\\([^\n]*\\)\n\\([^