type of NAME slot of thread-related datastructures

[Tobias C. Rittweiler]

The name of THREAD can be an arbitrary object.

The name of MUTEX, WAITQUEUE, SEMAPHORE must be
a simple-string if given.

The name of a SB-QUEUE:QUEUE can be an arbitrary object
again.

We should canonicalize this.

I'd suggest (OR NULL SYMBOL SIMPLE-STRING).

What would be an appropriate name for DEFTYPE'ing this?

[Tobias C. Rittweiler (tcr)]

I committed this in 1.0.37.30. The type expands to SIMPLE-STRING,
which may seem restrictive. However, the rationale is that I'm also
working on whostate support, to ultimatively provide something like
what can be seen here:

    http://paste.lisp.org/display/97347

However, it's crucial that this code does not cons (whostate is set
in GET-MUTEX, CONDITION-WAIT etc.) as that would be pretty
bad especially on our stop-the-world-gc bottleneck.

So I decided to restrict the type to simple-string so these names
can just be taken for automatic WHOSTATE computation without
having to cons up new strings due to prin1-to-string or something.