[PATCH] Simplify strncat.

[Roland McGrath]

Use '\0', not '\000'.

IIRC we have a general policy about having a benchtests case and citing
numbers on that.  But for strncat there is pretty universal agreement that
nobody should use it when they care about much of anything (including
performance), and the drastic simplification seems like a good thing.

With the cosmetic fix, I'm fine with this if nobody else objects.