NSUserDefaults update ... please test.

[Richard Frith-Macdonald]

OPENSTEP and MacOS-X explicitly warn that NSUserDefaults is not thread 
safe.

I have always thought that this was a bad thing, and the only 
justification
I could see for it was system performance - user defaults are used in 
many
places, so making them thread safe might have a big performance 
impact ...
on the other hand, they are used in a lot of places so having them not be
thread safe is asking for trouble.

Anyway, I've just tried adding locking to make them thread safe, and 
would like
impressions of what performance impact this has had.
I've therefore deliberately turned on locking even when the program is 
not
multi-threaded - so we can see what effect the locking is having.

Of course, this is quite a big change, so it's very possible I've not 
got it
100% working, but the testsuite passes.