[css-grid] Clarify inclusion of gutters in intrinsic size of grid container. Fixes #246.

Author: fantasai

css-grid/Overview.bs

@@ -799,11 +799,13 @@ Sizing Grid Containers</h3>
 	the <a>grid container</a>’s ''auto'' block size is its max-content size.
 
 	The <a>max-content size</a> of a <a>grid container</a> is
-	the sum of the <a>grid container’s</a> track sizes in the appropriate axis,
+	the sum of the <a>grid container’s</a> track sizes (including gutters)
+	in the appropriate axis,
 	when the grid is sized under a <a>max-content constraint</a>.
 
 	The <a>min-content size</a> of a <a>grid container</a> is
-	the sum of the <a>grid container’s</a> track sizes in the appropriate axis,
+	the sum of the <a>grid container’s</a> track sizes (including gutters)
+	in the appropriate axis,
 	when the grid is sized under a <a>min-content constraint</a>.
 
 	See [[!CSS3-SIZING]] for a definition of the terms in this section.