Fixes #10903 and #10457: IE8-9 don't support events on elements without...

Fixes #10903 and #10457: IE8-9 don't support events on elements without background-color, so we have to hack it

dist/css/bootstrap.css

@@ -730,7 +730,7 @@ address {
 }
 
 code,
-kdb,
+kbd,
 pre,
 samp {
   font-family: Monaco, Menlo, Consolas, "Courier New", monospace;
@@ -6439,6 +6439,8 @@ button.close {
   margin: 1px;
   text-indent: -999px;
   cursor: pointer;
+  background-color: #000 \9;
+  background-color: rgba(0, 0, 0, 0);
   border: 1px solid #ffffff;
   border-radius: 10px;
 }

less/carousel.less

@@ -160,6 +160,17 @@
     border: 1px solid @carousel-indicator-border-color;
     border-radius: 10px;
     cursor: pointer;
+
+    // IE8-9 hack for event handling
+    //
+    // Internet Explorer 8-9 does not support clicks on elements without a set
+    // `background-color`. We cannot use `filter` since that's not viewed as a
+    // background color by the browser. Thus, a hack is needed.
+    //
+    // For IE8, we set solid black as it doesn't support `rgba()`. For IE9, we
+    // set alpha transparency for the best results possible.
+    background-color: #000 \9; // IE8
+    background-color: rgba(0,0,0,0); // IE9
   }
   .active {
     margin: 0;