[whatwg] : removing the src="" content attribute

[Anne van Kesteren]

Currently it's only clear what should happen when you mutate the  
attribute. There's an assumption that there will be a new value which  
doesn't have to be the case. For instance, if the src="" attribute is  
removed.

--
Anne van Kesteren
<http://annevankesteren.nl/>
<http://www.opera.com/>