Bug 730559: Limit the number of columns during layout of column sets to prevent hang. [r=mats]
In nsRuleNode, when we parse a number of columns from a CSS style sheet, we enforce
a rule that the number of columns cannot exceed 1000. This patch simply enforces
the same rule when we decide that the column count will be generated based on
the available width (e.g. the column-count property has a value of 'auto').