Update of NSTableView

[Fred Kiefer]

I rewrote big parts of NSTableView to use NSIndexSet to store the 
selection. I also started to clean up the one big selectiob function, 
but didn't get to far here. I failed on my biggest goal, to remove at 
least 1000 lines of code from this file, I only got about 900. I am 
still very sure that there is more to remove, but don't have time for it 
right now, so feel free to pick this task up.

I tried to be very carefull with my cleanup, not to change anything that 
I did not understand, and there were loads in this category. There may 
still be a few changes in behaviour, if you find any please report them 
and I will try to correct them. There have been selecion problems before 
this change, don't expect them to go away with my change and please 
don't report them to me, rather you should try to clean them up yourself.

The methods [-selectColumnIndexes:byExtendingSelection:] and 
[-selectRowIndexes:byExtendingSelection:] are still missing, but should 
be easy to implement now.

Fred