Allow more characters in emphasis

* lisp/org.el (org-emphasis-regexp-components): Allow singe quote,
  double quote and comma as the last character in an emphasis string.

Reported-by: Marcin Borkowski <mbork@mbork.pl>
<http://permalink.gmane.org/gmane.emacs.orgmode/102191>

lisp/org.el

@@ -4364,7 +4364,7 @@ After a match, the match groups contain these elements:
 ;; set this option proved cumbersome.  See this message/thread:
 ;; http://article.gmane.org/gmane.emacs.orgmode/68681
 (defvar org-emphasis-regexp-components
-  '(" \t('\"{" "- \t.,:!?;'\")}\\[" " \t\r\n,\"'" "." 1)
+  '(" \t('\"{" "- \t.,:!?;'\")}\\[" " \t\r\n" "." 1)
   "Components used to build the regular expression for emphasis.
 This is a list with five entries.  Terminology:  In an emphasis string
 like \" *strong word* \", we call the initial space PREMATCH, the final