LaTeX export: Fix two bugs.

1.  When LaTeX export was done with a time-stamped file, a format
    error in the timestamp format caused the output file to not
    have the % comment in front of the time string.  As this line
    is early in the file, a LaTeX error would result.

2.  Replacement of some special characters could fail.  Strangely
    this shows up only in XEmacs, but it still is a bug.

Both bugs were reported by Hugh Daschbach.

lisp/ChangeLog

@@ -1,3 +1,10 @@
+2008-12-21  Carsten Dominik  <carsten.dominik@gmail.com>
+
+	* org-export-latex.el (org-export-latex-make-header): Double the %
+	in the time stamp format.
+	(org-export-latex-special-chars): Handle case where there is no
+	match group 3.
+
 2008-12-20  Carsten Dominik  <carsten.dominik@gmail.com>
 
 	* org.el (org-get-refile-targets, org-refile-get-location): Use

lisp/org-export-latex.el

@@ -689,7 +689,7 @@ OPT-PLIST is the options plist for current buffer."
 	(author (plist-get opt-plist :author)))
     (concat
      (if (plist-get opt-plist :time-stamp-file)
-	 (format-time-string "% Created %Y-%m-%d %a %H:%M\n"))
+	 (format-time-string "%% Created %Y-%m-%d %a %H:%M\n"))
      ;; insert LaTeX custom header
      org-export-latex-header
      "\n"
@@ -913,7 +913,8 @@ See the `org-export-latex.el' code for a complete conversion table."
 		       (replace-match (or (save-match-data
 					    (org-export-latex-treat-backslash-char
 					     (match-string 1)
-					     (match-string 3))) "") t t))
+					     (or (match-string 3) "")))
+					  "") t t))
 		      ((member (match-string 2) '("_" "^"))
 		       (replace-match (or (save-match-data
 					    (org-export-latex-treat-sub-super-char