[css3-text] tab processing

Section "3.3.  The White Space Processing Rules", contains this:

"Each tab is rendered as a horizontal shift that lines up the start edge  
of the next glyph with the next tab stop. Tab stops occur at points that  
are multiples of the width of a space (U+0020) rendered in the block's  
font from the block's starting content edge. How many spaces is given by  
the ‘tab-size’ property."

This used to be true when tab-size only took <integer> as a value, but it  
now also take <length>. This text should be amended to reflect that.

  - Florian