proposal: disable tcache when using malloc_check

[Florian Weimer]

* DJ Delorie:

> This is a fairly trivial change with significant side effects.  The
> idea is that when one is using malloc_check (via tunables or environ)
> correctness and paranoia are favored over performance.  Thus, as
> tcache bypasses all the malloc_check semantics, it should be disabled
> therein so that every malloc/free/etc get the full malloc_check
> treatment.
>
> Does anyone have any opinions for or against this idea?
>
> 	* malloc/hooks.c (__malloc_check_init): Disable tcache.

I think it's the right thing to do.

Thanks,
Florian