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

…n commit ed15f2f improves the outputfunction excelHtml5 to export excel files with multi-row headers, without the merges. On top of what is described  rstudio#418, it makes other modifications needed to match the latest rstudio/DT version.

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

@@ -52,9 +52,9 @@
     }
 
     function K(a, b) {
-        var d =
-            a.header[b].length,
-            c;
+        //var d = a.header[b].length        
+        for (var d = 0, o = 0; o<a.header.length; o++) d = Math.max(d, a.header[o][b].length); // gets the largest width of column b
+        var c;
         a.footer && a.footer[b].length > d && (d = a.footer[b].length);
         for (var f = 0, g = a.body.length; f < g; f++)
             if (c = a.body[f][b], c = null !== c && c !== s ? c.toString() : "", -1 !== c.indexOf("\n") ? (c = c.split("\n"), c.sort(function(a, c) {
@@ -441,17 +441,27 @@
                     i("row:eq(" + (a - 1) + ") c", e).attr("s", "51")
                 },
                 p = b.buttons.exportInfo(c);
-            p.title && (r([p.title], g), k(g, d.header.length - 1));
+            p.title && (r([p.title], g), k(g, /*d.header.length*/ d.header[d.header.length - 1].length - 1));
             p.messageTop && (r([p.messageTop],
-                g), k(g, d.header.length - 1));
-            c.header && (r(d.header, g), i("row:last c", e).attr("s", "2"));
+                g), k(g, /*d.header.length*/ d.header[d.header.length - 1].length - 1));
+            /* ----- BEGIN added Code ----- */
+            //c.header && (r(d.header, g), i("row:last c", e).attr("s", "2"));
+
+			if(c.header){
+				for (o = 0; o < d.header.length; o++){
+	                  r(d.header[o], g);
+	                  i("row:last c", e).attr("s", "2");
+	                }
+            }
+
+            /*END added code*/
             for (var o = 0, u = d.body.length; o < u; o++) r(d.body[o], g);
             c.footer && d.footer && (r(d.footer, g), i("row:last c", e).attr("s", "2"));
-            p.messageBottom && (r([p.messageBottom], g), k(g, d.header.length - 1));
+            p.messageBottom && (r([p.messageBottom], g), k(g, /*d.header.length*/d.header[d.header.length - 1].length - 1));
             r = q(e, "cols");
             i("worksheet", e).prepend(r);
             k = 0;
-            for (o = d.header.length; k < o; k++) r.appendChild(q(e, "col", {
+            for (o = /*d.header.length*/d.header[d.header.length - 1].length; k < o; k++) r.appendChild(q(e, "col", {
                 attr: {
                     min: k + 1,
                     max: k + 1,