Relax the match criteria for MathML header line

* lisp/org.el (org-create-math-formula): Allow the xmlns attribute to
  be preceded by any other mathml header attribute.

The problem here was that the match criteria for MathML assumed that
the xmlns attribute is the first listed in the top level MathML <math>
element.  Some LaTeX -> MathML converters (e.g., pandoc) will add
attributes before xmlns, which is still valid MathML.

lisp/org.el

@@ -19386,12 +19386,9 @@ inspection."
 	    (with-current-buffer (find-file-noselect tmp-out-file t)
 	      (goto-char (point-min))
 	      (when (re-search-forward
-		     (concat
-		      (regexp-quote
-		       "<math xmlns=\"http://www.w3.org/1998/Math/MathML\"")
-		      "[^>]*?>"
-		      "\\(.\\|\n\\)*"
-		      "</math>")
+		     (format "<math[^>]*?%s[^>]*?>\\(.\\|\n\\)*</math>"
+			     (regexp-quote
+			      "xmlns=\"http://www.w3.org/1998/Math/MathML\""))
 		     nil t)
 		(prog1 (match-string 0) (kill-buffer))))))
     (cond