Fix: Arrays in settings object shared between instances

- Because of the way _fnExtend() was deep copying objects, but shallow
  copying (i.e. references) arrays, the arrays used in the settings
  object were actually being shared between all instances of DataTables
  on a page.

- This is most noticable in the column filtering, whereby if you apply
  a filter to the column of one table, it is applied to all tables!

- The fix is to dump _fnExtend and replace it with a typical jQuery
  extend. However, one special consideration is made for the data being
  passed it - we absolutely do want that reference to be retained (that
  + the fact that extend is slow on large arrays/objects) so it is
  dumped into a temp variable which is then assigned back to the cloned
  object.

- This fixed DataTables/DataTables issue #213