NSBrowser patch

[Benhur Stein]

Hi.
Here is my promissed (and delayed) patch to NSBrowser.
It fixes the bug of not opening a NSOpen/SavePanel with a selected
file in some situations, and also fixes many problems with
keyboard navigation.
I would have commited it, but maybe it is better that somebody
take a look at it before.
I will be out of town for a week, so if someone want to commit it
before, please go ahead.

Benhur