Preserve math environments in title when exporting to LaTeX

* lisp/org-latex.el (org-export-as-latex): Sent the section title
through the preprocessor.

Hi all,

This patch fixes the issue I originally described here:
http://article.gmane.org/gmane.emacs.orgmode/32281

It preserves math-mode delimiters (e.g. "$" and "\(") in the document
title when exporting to LaTeX.  (That is, it prevents them from being
escaped, by running the title through org-export-preprocess-string,
which marks them with the org-protected property.)  It should work
regardless of whether the title is pulled from a headline, from the text
before the first headline, or from an explicit #+TITLE declaration.

(This is my first time contributing a patch to a Free Software project
-- so please, let me know what you think!)

Best,
Richard

lisp/org-latex.el

@@ -729,13 +729,33 @@ when PUB-DIR is set, use this as the publishing directory."
 	 (org-current-export-file buffer-file-name)
 	 (title (or (and subtree-p (org-export-get-title-from-subtree))
 		    (plist-get opt-plist :title)
-		    (and (not
-			  (plist-get opt-plist :skip-before-1st-heading))
-			 (org-export-grab-title-from-buffer))
+		    (unless (plist-get opt-plist :skip-before-1st-heading)
+		      (let ((pt (org-export-grab-title-from-buffer)))
+			(remove-text-properties 0 (length pt)
+						'(:org-license-to-kill t) pt)
+			pt))
 		    (and buffer-file-name
 			 (file-name-sans-extension
 			  (file-name-nondirectory buffer-file-name)))
 		    "No Title"))
+	 ; Preprocessing preserves math environments in title
+	 (title
+	  (and title (string-match "\\S-" title)
+	       (org-export-preprocess-string
+		title
+		:emph-multiline t
+		:for-LaTeX t
+		:comments nil
+		:tags (plist-get opt-plist :tags)
+		:priority (plist-get opt-plist :priority)
+		:footnotes (plist-get opt-plist :footnotes)
+		:drawers (plist-get opt-plist :drawers)
+		:timestamps (plist-get opt-plist :timestamps)
+		:todo-keywords (plist-get opt-plist :todo-keywords)
+		:add-text nil
+		:select-tags nil
+		:exclude-tags nil
+		:LaTeX-fragments nil)))
 	 (filename
 	  (and (not to-buffer)
 	       (concat