Update on freeze status of glibc 2.18?

[Roland McGrath]

> The way I read Roland's comment is that independently of whether things
> are controlled via a configure switch instead of an env var, they should
> not diverge from the API or ABI guarantees (and this includes the POSIX
> guarantees such as the relock case requirements for
> PTHREAD_MUTEX_NORMAL).  Roland, is that correct?

Correct.  This also means not introducing new API or ABI features.