Sped up DataTable loading when heavy sorting is involved

[Brilliand]

Had some trouble with "api.rows().invalidate()" causing
an exponentially increasing slowdown when loading a
heavily reordered table. Changed _fnOrderColumns to
call that function (and a few other "refresh all" functions)
only once.

[DataTables]

Thanks very much for this. I haven't looked through the change yet (there is quite a lot of additional code it looks like), but just to say that the error with DataTables invalidation function should be fixed in the current nightly ( https://github.com/DataTables/DataTables/tree/master/media/js ) if you fancy giving it a go.

[Brilliand]

The extra code is mostly a copy-paste of fnColReorder - it's just different enough that there was no obvious way to keep that one function suitable for both purposes. The code duplication could probably be reduced quite a bit, though.

[719media]

I ran into this issue, and it is really bad lockup.

I created an updated/easier to merge #57, which I'm sure can be improved upon by someone who is more familiar with the code.