Description

The initial check

	if(unique != undefined && unique == false) {

can be simplified to

	if(unique === false) {

I.e. the function may look like this:

Array.prototype.pushUnique = function(item,unique)
{
	if(unique === false) {
		this.push(item);
	} else {
		if(this.indexOf(item) == -1)
			this.push(item);
	}
};