Merge mfairchild365's contributions regarding absolute positioning (#99, unl#1) into master:

Make absolutely positioned contrast errors warnings.
We can't reliably compute the contrast of text over a background if the text is absolutely positioned over the background of another element that isn't a direct parent of the text element.

Conflicts:
	Standards/WCAG2AAA/Sniffs/Principle1/Guideline1_4/1_4_3.js
	Standards/WCAG2AAA/Sniffs/Principle1/Guideline1_4/1_4_3_Contrast.js