Unmark buffer modified at markdown-unfontify-region-wiki-links (#146)

In Emacs 24.3 some `remove-text-properties` calls, like the ones in
`markdown-unfontify-region-wiki-links`, mark the buffer modified. This
function is invoked by default from `markdown-mode`, and so it makes
that a Markdown buffer is marked modified just by visiting a file or
changing to this major mode.

This change unsets the buffer modified mark if it wasn't previously set.

markdown-mode.el

@@ -6274,8 +6274,12 @@ See `markdown-wiki-link-p' and `markdown-follow-wiki-link'."
 (defun markdown-unfontify-region-wiki-links (from to)
   "Remove wiki link faces from the region specified by FROM and TO."
   (interactive "*r")
-  (remove-text-properties from to '(font-lock-face markdown-link-face))
-  (remove-text-properties from to '(font-lock-face markdown-missing-link-face)))
+  (let ((modified (buffer-modified-p)))
+    (remove-text-properties from to '(font-lock-face markdown-link-face))
+    (remove-text-properties from to '(font-lock-face markdown-missing-link-face))
+    ;; remove-text-properties marks the buffer modified in emacs 24.3,
+    ;; undo that if it wasn't originally marked modified
+    (set-buffer-modified-p modified)))
 
 (defun markdown-fontify-region-wiki-links (from to)
   "Search region given by FROM and TO for wiki links and fontify them.