Fixes server-side loading on column visibility change

When showing or hiding a column toggle a server side refresh.

Based on the messages posted in [this forum thread](http://datatables.net/forums/discussion/12632/colvis-prevent-refresh-on-serverside-table-unles-re-sorted-or-page-changed/p1) I was able to identify the underlying problem to prevent server-side refresh.

The initial comment of allan "paved" the way to make this correction.