[whatwg] Handling of collapsed whitespace in contenteditable

There's a very good reason why existing browser engines have to resort 
to   hacks.  It's the only practical way to make sure that 
"foo__bar" (s/_/ /) entered into an editable element would appear the 
intended way when the innerHTML of the editable area is submitted to a 
server and later displayed in another documents.

For this reason, I think we should make the sad choice of specifying the 
latter behavior.

Cheers,
Ehsan