Empty paragraphs should not be displayed even if they have styles applied to them

To reproduce:

• In wiki mode type

  (% style="color: blue; text-align: center;" %)
  Hello world
  

• In wysiwyg editor, move cursor to space between "Hello" and "world" and type return several times (say 3 times)
• Save

You'll see the following in wiki mode:

(% style="color: blue; text-align: center;" %)
Hello 


(% style="color: blue; text-align: center;" %)



(% style="color: blue; text-align: center;" %)



(% style="color: blue; text-align: center;" %)
world

I don't know yet where this should be fixed:

• in the XHTML parser
• in the HTML cleaner
• in the editor itself