display: inline-block for .errorbox, .warningbox, .successbox

It previously used float: left to generate a box with intrinsic width,
which required the next element to have clear: left to avoid display
quirks. display: inline-block is the proper way to do this.

Includes hacks for IE6 and FF2.

Bug: 33438
Change-Id: Ibb9371eecb99b627ba9dfca5b0a60143fbd6f84f