Fixes #11561: Add float: left; to .form-control within input groups to prevent IE9 from screwing up placeholder text and select menu arrows

less/input-groups.less

@@ -17,6 +17,11 @@
   }
 
   .form-control {
+    // IE9 fubars the placeholder attribute in text inputs and the arrows on
+    // select elements in input groups. To fix it, we float the input. Details:
+    // https://github.com/twbs/bootstrap/issues/11561#issuecomment-28936855
+    float: left;
+
     width: 100%;
     margin-bottom: 0;
   }