The man-page for pthread_setspecific does not define the EAGAIN return value.
Further without this patch it was not possible to set keys that have been
already set a new value.
Add test for setting a new value to a already set key.
Formerly POSIX keys were only enabled when POSIX threads
were enabled. Because they are a truly safe alternative
to per-task variables in an SMP system, they are being
enabled in all configurations.
This patch enables unlimited model in POSIX key manger and have a decent
runtime on POSIX key searching, adding and deleting operations. Memory
overhead is lower than current implementation when the size of key and key
value becomes big.
