#50 OAA rule 15/16 : contrast ratio >= or > ?

[goetsu]

Hi,

WCAG2 1.4.3 say that the contrast ratio must be "at least" x.x
and the techniques say : "Check that the contrast ratio is equal to or
greater than x.x"
(http://www.w3.org/TR/2010/NOTE-WCAG20-TECHS-20101014/G18 for example)

The current rules test if the ratio is "> x" so I propose to change it
to ">= x"

Futhermore I don't think that the rules is checking the font size of the
element to determine if it's a large text or not, so we need to :
- mark the two rules as "potential violation" not "violation".
- a new test to check the 7:1 ratio for text regarding 1.4.6 criteria