pthread_key_{create,delete} pthread_{g,s}etspecific on NetBSD

[christos%zoulas.com@localhost (Christos Zoulas)]

If you read the comments on pthread_tsd.c, we chose a naive and simple
implementation of those functions, one that chooses not to invalidate
values of keys in other threads when pthread_key_delete() is called.
This breaks chromium, which expects pthread_key_delete() to do cleanup
in all threads. I put a patch on:

    http://www.netbsd.org/~christos/pthread_key.diff

that changes this. Please comment.

christos