Checks the availability of the specified page. Terminates performing of the task, if the page was unavailable.
checkAvailability = function(aPage, aExpectedIP, aIncludedText, aUserAgent);
checkAvailability = function(aCheckItems);
checkAvailability('habrahabr.ru');
checkAvailability('habrahabr.ru', '178.248.233.33');
checkAvailability('habrahabr.ru', '178.248.233.33', 'habr');
checkAvailability([ {"page":"habrahabr.ru","expectedIP":"178.248.233.33","includedTextt":"habr"}, {"page":"liveinternet.ru","includedText":"stat","userAgent":"my ua"} ]);