[css3-values] whitespace requirement around + and - in calc()

http://dev.w3.org/csswg/css3-values/#the-calc-min-and-max-functions
no longer has the requirement (which I believe used to be in the
spec, and which I believe the WG agreed on) that there must be
whitespace around the '+' and '-' inside of calc().

(This is needed because '-' is an identifier character in CSS, so
3em-2px tokenizes as a length with number '3' and unit 'em-2px'.)

-David

-- 
L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/