Thread IDs on BSD

[Richard Frith-Macdonald]

I don't have BSD systems to test on, but I've added code which should report 
the BSD thread ID of a thread in NSLog output, and also modified the 
-description method of NSThread so that it should report thread name and is as 
it does on OSX in the form '<NSThread: 0x....>{name = X, num = Y}'
Please could anyone with BSD systems have a look at the latest code in svn.

As an easy way to check ... the regression test in Tests/base/NSThread should 
print the description of a thread in its log output.