Add "clear:right" to right-floating thumbnails, and "clear:left" to left-floating...

Add "clear:right" to right-floating thumbnails, and "clear:left" to left-floating ones.

This solves a problem we've had for some time: Two right-floating images with too little text
between them cascade inwards into the middle of the page. Adding more text isn't a viable
solution because "too little text" is more and more text with increasing screen resolution. This
solves it elegantly, I think. Also, since the 'clear' is added only to the right-floating
elements, this does *not* push the text down and does *not* cause blocks of whitespace to occur.