Combine horizontalDefault and verticalDefault to one variable - possibly named center

Variables 'horizontalDefault' and 'verticalDefault' are both set initially to the string "center" and never modified. Consider combining these into a single variable.

old:

var horizontalPositions = /left|center|right/,
	horizontalDefault = "center",
	verticalPositions = /top|center|bottom/,
	verticalDefault = "center",
	_position = $.fn.position,
	_offset = $.fn.offset;

new:

var horizontalPositions = /left|center|right/,
	verticalPositions = /top|center|bottom/,
	center = "center",
	_position = $.fn.position,
	_offset = $.fn.offset;