Fix conflict with bootstrap 2.x icon style. 

In bootstrap 2.0.3, the icon style is:

```
[class^="icon-"],
[class*=" icon-"] {
  display: inline-block;
  width: 14px;
  height: 14px;
  *margin-right: .3em;
  line-height: 14px;
  vertical-align: text-top;
  background-image: url("img/glyphicons-halflings.png");
  background-position: 14px 14px;
  background-repeat: no-repeat;
}
```

And I found the `vertical-align` and `background-image` will break the display of the icon.