ie support placeholder color (http://msdn.microsoft.com/en-us/library/ie/hh772745(v=vs.85).aspx)

Author: ademaro

less/mixins.less

@@ -84,6 +84,9 @@
   :-moz-placeholder {
     color: @color;
   }
+  :-ms-input-placeholder {
+    color: @color;
+  }
   ::-webkit-input-placeholder {
     color: @color;
   }