[PATCH] support: Implement <support/descriptors.h> to track file descriptors

[Florian Weimer]

* Florian Weimer:

> * Carlos O'Donell:
>
>> On 11/29/18 11:43 PM, Florian Weimer wrote:
>>> I could try to count more precisely how many bytes are actually needed,
>>> but that seemed like a waste of mental resources.  Should I use
>>> xasprintf instead, to make clear that there is no truncation?
>>
>> Yes, I think xasprintf solves all the problems.
>
> Like this?
>
> I also enhanced the test to test more conditions in the list merging
> code.

Any further comments?  I would like to commit this.

Thanks,
Florian