Log Message:
Update to 4.13

Changelog:
NSPR 4.13 has the following bug fixes:

* PL_strcmp (and others) were fixed to return consistent results
  when one of the arguments is NULL.

* PollEvent was fixed to not block on clear.

* Pipes are always nonblocking.

* PR_GetNameForIdentity: added thread safety lock and bound checks.

* Removed the PLArena freelist.

* Avoid some integer overflows.

* fixed several comments.

For the full list see:
https://bugzilla.mozilla.org/buglist.cgi?resolution=FIXED&query_format=advanced&product=NSPR&target_milestone=4.13