added padding to scrollDistance rounding function to be able to sort values in GA

Since this value is a label (string), you have to add some padding to be able to sort it in proper order in GA - other way you'll get:
1000
10000
2000
so basically it'll be sorted alphabetically.
before: https://www.dropbox.com/s/zvkldu7lnbv5vfu/Screenshot%202014-08-07%2011.25.38.jpg
after: https://www.dropbox.com/s/mlcxvzc1jb5bapm/Screenshot%202014-08-07%2011.48.12.jpg
less readable but sortable


i've tried with zeros at first but it was completely unreadable: https://www.dropbox.com/s/hiukj8bwucb6s8t/Screenshot%202014-08-07%2011.29.40.jpg

padding solution from:
http://stackoverflow.com/a/9744576/465064
(fastest and most elegant one)