According to rstudio#418, improve buttons.html5.min.js. This builds o…

…n commit ed15f2f allowing the outputfunction pdfHtml5 to print pdf with multi-row headers

inst/htmlwidgets/lib/datatables-extensions/Buttons/js/buttons.html5.min.js

@@ -497,12 +497,24 @@
             var d = b.buttons.exportData(c.exportOptions),
                 a = b.buttons.exportInfo(c),
                 f = [];
-            c.header && f.push(i.map(d.header, function(a) {
+            /* ----- BEGIN added Code ----- */
+            /*c.header && f.push(i.map(d.header, function(a) {
                 return {
                     text: "string" === typeof a ? a : a + "",
                     style: "tableHeader"
                 }
             }));
+            */
+            if(c.header){
+	            for(g = 0; g < d.header.length; g++)
+		            f.push(i.map(d.header[g], function(a) {
+		                return {
+		                    text:  "string" ===  typeof a ? a : a + "",
+		                    style: "tableHeader"
+		                }
+		            }));
+	    	}
+	    	/*END added code*/
             for (var g = 0, e = d.body.length; g < e; g++) f.push(i.map(d.body[g], function(a) {
                 return {
                     text: "string" === typeof a ? a : a + "",